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Inheritance

1

Non-Mendelian inheritance HP:0001426

Podoconiosis is inherited as a susceptibility, not as a disease. A segregation analysis of multi-generational Ethiopian families fitted an autosomal co-dominant major-gene model with a sibling recurrence risk ratio of 5.07 and heritability of 0.63; two subsequent genome-wide association studies located the signal in the HLA class II region and found nothing outside it. The entry binds `HP:0001426` rather than `HP:0032113` (Semidominant inheritance) because the latter sits under *Mendelian inheritance* in HPO, and no genotype produces podoconiosis without the soil exposure.

complex HLA class II-associated susceptibility

Show evidence (2 references)

PMID:33558538 SUPPORT Human Clinical

"A segregation analysis of 59 multi-generational podoconiosis families from the Wolaita ethnic group in southwest Ethiopia indicated an autosomal co-dominant pattern of inheritance with an estimated sibling recurrence risk ratio (λs) and heritability of 5.07 and 0.63 respectively"

The segregation model, the sibling recurrence risk ratio and the heritability estimate, all in one sentence.

PMID:22455414 SUPPORT Human Clinical

"Podoconiosis is a tropical lymphedema resulting from long-term barefoot exposure to red-clay soil derived from volcanic rock. The World Health Organization recently designated it as a neglected tropical disease. Podoconiosis develops in only a subgroup of exposed people, and studies have shown..."

Confirms the 63% heritability independently, and states in the same breath that the disease develops only in exposed people.

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Discussions and Knowledge Gaps

3

Which constituent of alkalic volcanic red clay is the trigger, and how does a mineral particle come to be presented by an HLA class II molecule?

KNOWLEDGE GAP podo_soil_trigger_unidentified

Attached to

pathophysiology#Lymphatic Transport of Particle-Laden Macrophages pathophysiology#HLA Class II-Restricted CD4 T-Cell Response environmental#Long-term barefoot contact with red-clay soil derived from alkalic volcanic rock

This is the hole at the centre of the disease. The exposure is known, the susceptibility locus is known and replicated, and the lesion is described in detail - but the antigen is not identified, and no mechanism connects a silicate particle to class II presentation. Kaolinite, smectite, quartz, iron oxides, beryllium and zirconium are all correlated with endemicity and none is established as causal; the systematic review that assembled them says outright that they may be covariates. Without the trigger there is no biomarker, no early diagnostic, and no target - which is why the entry's edge from particle transport to the HLA node is curated with unknown intermediates rather than as antigen presentation.

Why do healthy exposed controls mount a larger IL-1beta response to kaolinite and chlorite than patients do?

INTERPRETATION podo_inverted_mineral_response

Attached to

pathophysiology#Chronic Systemic Immune Activation

The intuitive model - patients are hypersensitive to the mineral - is contradicted by the only in vitro stimulation study in this disease. Patients had higher unstimulated TNF-alpha and IL-1beta, but on stimulation the controls produced two to three times more IL-1beta. The authors read this as persistent in vivo activation, with exhaustion or regulation blunting the response to a further hit. The entry curates the result as a SUPPORT item on the immune-activation node - it supports that node's chronic-activation reading, and `supports` is relative to the record an item sits on rather than to the hypothesis the result rules out. It is curated rather than omitted because an entry that quietly dropped it would imply a hypersensitivity model the evidence does not support. It is a single small study and should not be treated as settled either way.

Can any existing model system reproduce podoconiosis, given that the disease requires both a human HLA class II haplotype and barefoot bipedal soil contact?

HUMAN MODEL MISMATCH podo_no_animal_model

Attached to

pathophysiology#HLA Class II-Restricted CD4 T-Cell Response animal_models#Rabbit

The only experimental model in the literature injects silica directly into lymphatics, which reproduces the vessel lesion while bypassing the skin, the exposure route, the mineral species and the susceptibility genotype. There is no animal that walks barefoot on volcanic clay carrying a human class II risk haplotype, and no natural veterinary counterpart has been described. So every mechanistic claim upstream of the lymphatic vessel in this entry rests on human tissue and human genetics alone, and the one model available cannot arbitrate between the HLA-dependent and HLA-independent routes to the same lesion.

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Pathophysiology

13

Chronic Barefoot Contact with Alkalic Volcanic Clay Soil

The necessary exposure. Subsistence farmers working barefoot on red clay weathered from alkalic volcanic bedrock accumulate contact over years to decades. The soil is the operative agent, not the terrain: endemicity tracks bedrock geochemistry and the pedogenic conditions that produce these clays - high altitude and high rainfall - rather than any vector distribution.

Downstream

Transdermal Entry of Silicate Mineral Particles

Show evidence (3 references)

PMID:22455414 SUPPORT Human Clinical

"Podoconiosis is a tropical lymphedema resulting from long-term barefoot exposure to red-clay soil derived from volcanic rock. The World Health Organization recently designated it as a neglected tropical disease. Podoconiosis develops in only a subgroup of exposed people, and studies have shown..."

States the exposure and its duration, which is what this node records, and the heritability figure that makes the exposure necessary rather than sufficient.

PMID:40623043 SUPPORT Human Clinical

"Nine studies found a correlation between podoconiosis occurrence and regions with underlying alkalic volcanic bedrock, and six linked pedogenic factors (altitude and rainfall) with disease occurrence. Several studies linked specific soil mineralogy and geochemistry with endemic regions,..."

The systematic review's bedrock and pedogenic correlations, and the mineral inventory that the next node's particles come from.

PMID:37719165 SUPPORT Human Clinical

"Walking barefoot adjusted odd ratio (AOR) 5.35 (95% CI: 1.65, 9.05), p = 0.001, not washing feet with soap and water regularly AOR 2.8 (95% CI: 1.16, 4.44, p = 0.001), and an increased age AOR 2.23 (95% CI: 1.25, 5.58) were factors significantly associated with the prevalence of podoconiosis."

The effect estimate for the behaviour itself - walking barefoot carries an adjusted odds ratio above five in pooled sub-Saharan data.

Transdermal Entry of Silicate Mineral Particles

Colloid-sized silicate particles cross the plantar and dorsal skin of the foot and lodge in the dermis. Their identity is partly known and partly not: kaolinite predominates in lymph node microanalysis at 0.2-2 micrometres, and endemic soils are enriched in smectite, mica, quartz, iron oxides, beryllium and zirconium - but which constituent is the operative trigger has never been established.

dermis of the foot UBERON:0002067

Downstream

Macrophage Phagocytosis of Mineral Particles

Show evidence (2 references)

PMID:2604475 SUPPORT Human Clinical

"The presence of microparticles of clay is demonstrated in the dermis of the foot in a patient with endemic elephantiasis. The particles are seen to be in the phagosomes of macrophages or in the cytoplasm of other cells."

The direct demonstration that clay microparticles are present in the dermal tissue of an affected foot.

PMID:39591258 SUPPORT Other

"The predominant silica particles were mainly of the kaolinite type, sized between 0.2 and 2 µm"

Gives the dominant mineral species and its size range, which is what makes transdermal entry mechanically plausible. Graded OTHER because the sentence is this paper's summary of the earlier microanalysis literature, not its own measurement.

Macrophage Phagocytosis of Mineral Particles

Dermal macrophages engulf the silicate particles. This step is not itself pathological - particles are found in the lymph nodes of unaffected residents of endemic areas too, which is why the entry treats deposition as necessary and the host response as what separates disease from exposure.

dermal macrophage CL:0000235

phagocytosis GO:0006909 ↑ INCREASED

dermis of the foot UBERON:0002067

Downstream

Lymphatic Transport of Particle-Laden Macrophages

Show evidence (2 references)

PMID:2604475 SUPPORT Human Clinical

"The presence of microparticles of clay is demonstrated in the dermis of the foot in a patient with endemic elephantiasis. The particles are seen to be in the phagosomes of macrophages or in the cytoplasm of other cells."

The particles inside macrophage phagosomes, which is precisely this node's claim.

PMID:22455414 SUPPORT Human Clinical

"The disease develops in only some people exposed to irritant soils, although mineral particles can be seen in the lymphatic system and lymph nodes of unaffected as well as affected people."

The observation that makes this node insufficient on its own: particles are present in unaffected people too. Curated here because it is the reason the HLA node exists.

Lymphatic Transport of Particle-Laden Macrophages

Particle-laden macrophages migrate into the lower-limb lymphatic vessels and on to the regional lymph nodes, where the silicates are recoverable by microanalysis. From here the chain forks: one arm needs the HLA class II susceptibility, the other does not.

lower-limb lymphatic vessel UBERON:0001473

Downstream

HLA Class II-Restricted CD4 T-Cell Response How a mineral particle comes to be presented on an HLA class II molecule is the central unsolved step in this disease, so the edge is curated with unknown intermediates rather than asserted as antigen presentation.

Endolymphangitis Silica delivered directly into a lymphatic provokes macrophage reaction and fibrosis in the vessel wall without requiring the adaptive arm, which is the second, HLA-independent route to the same lesion.

Show evidence (2 references)

PMID:22455414 SUPPORT Human Clinical

"mineral particles in red-clay soils are absorbed through the skin of the foot and engulfed by macrophages in the lower limb lymphatic system, inducing an inflammatory response in the lymphatic vessels, which results in fibrosis and obstruction of the vessel lumen."

States the transport-to-lymphatics model this node represents, and names the inflammatory consequence the downstream nodes carry.

PMID:39591258 SUPPORT Other

"Silicate particles of the kaolinite and aluminum types have been identified in femoral lymph node biopsy samples from endemic area residents, suggesting a possible role in the pathogenesis of podoconiosis."

Locates the particles in femoral lymph node biopsies, the endpoint of the transport this node describes. Graded OTHER: background prose citing the earlier microanalysis literature, not this study's own result.

HLA Class II-Restricted CD4 T-Cell Response

The susceptibility step. Genome-wide association in Ethiopian populations places the signal squarely in the HLA class II region, replicated across three ethnic groups and with no other locus reaching significance in a better-powered second study. A class II association in a non-communicable disease is read as a CD4 T-cell-mediated response - but the antigen itself is unidentified, and whether the mineral is presented, modifies a self peptide, or binds the groove directly is unknown. Berylliosis is the explicit comparator.

CD4-positive T cell CL:0000624

HLA-DQA1 hgnc:4942 HLA-DRB1 hgnc:4948 HLA-DQB1 hgnc:4944

antigen processing and presentation via MHC class II GO:0019886 ↑ INCREASED

Downstream

Chronic Systemic Immune Activation

Show evidence (7 references)

PMID:22455414 SUPPORT Human Clinical

"We found a genomewide significant association of podoconiosis with the single-nucleotide polymorphism (SNP) rs17612858, located 5.8 kb from the HLA-DQA1 locus (in the allelic model: odds ratio, 2.44; 95% confidence interval [CI], 1.82 to 3.26; P=1.42×10(-9); and in the additive model: odds..."

The genome-wide significant signal that anchors this node, with its effect size.

PMID:22455414 SUPPORT Human Clinical

"HLA typing showed the alleles HLA-DRB1*0701 (odds ratio, 2.00), DQA1*0201 (odds ratio, 1.91), and DQB1*0202 (odds ratio, 1.79) and the HLA-DRB1*0701-DQB1*0202 haplotype (odds ratio, 1.92) were risk variants for podoconiosis."

The classical HLA typing behind the SNP association, naming the risk alleles and the haplotype.

PMID:22455414 SUPPORT INDIRECT Human Clinical

"Association between variants in HLA class II loci with podoconiosis (a noncommunicable disease) suggests that the condition may be a T-cell-mediated inflammatory disease and is a model for gene-environment interactions that may be relevant to other complex genetic disorders."

Graded INDIRECT because the T-cell interpretation follows from the class II association by inference; the authors state it as a suggestion, and no antigen-specific T-cell response has been demonstrated.

+ 4 more references

Chronic Systemic Immune Activation

Patients carry a measurably activated immune system at rest: raised HLA-DR on circulating CD4 and CD8 T cells, raised CD40 and CD86 on monocytes and dendritic cells, lower CD62L, and higher unstimulated TNF-alpha and IL-1beta than endemic controls. The activation is systemic, not confined to the affected limb.

monocyte CL:0000576 dendritic cell CL:0000451

inflammatory response GO:0006954 ↑ INCREASED

Downstream

Endolymphangitis The systemic activation is measured in blood and the lesion is in the limb lymphatics; no study connects the two directly, so the edge is curated with unknown intermediates. The direction is assumed, not shown: every cited measurement is cross-sectional case-control, and systemic activation is at least as plausibly a consequence of chronic lesional inflammation and recurrent acute attacks as a cause of them.

Show evidence (5 references)

PMID:38448477 SUPPORT Human Clinical

"Peripheral blood immunophenotyping of T cells indicated podoconiosis patients had significantly higher CD4 and CD8 T cell surface HLA-DR expression compared to healthy controls while CD62L expression was significantly lower."

The T-cell activation phenotype this node records, against endemic healthy controls.

PMID:38448477 SUPPORT Human Clinical

"The levels of the activation markers CD40 and CD86 were significantly higher on monocytes and dendritic cell subsets in patients compared to the controls."

The antigen-presenting-cell arm of the same activation state.

PMID:38448477 SUPPORT Human Clinical

"Our finding provides evidence that podoconiosis is associated with high levels of immune activation and inflammation with over-expression of genes within the pro-inflammatory axis."

The study's summary claim, which is what this node asserts.

+ 2 more references

Endolymphangitis

Inflammation of the lymphatic vessel wall, with subendothelial oedema and a lymphoplasmacytic infiltrate. This is the lesion the two upstream arms - the HLA-restricted response and the direct particle effect - converge on.

lymphatic vessel endothelial cell CL:0002138

lymphatic vessel of the lower limb UBERON:0001473

Animal models

Intralymphatic silica injection model Rabbit partially recapitulates Silica provoked immediate intense macrophage reaction and later fibrosis within lymph vessels, with lymphographic obstruction attributable more to the vessels than to the nodes.

Downstream

Lymphatic Vessel Wall Collagenization

Show evidence (3 references)

PMID:3006293 SUPPORT Model Organism

"Intralymphatic silica provoked an immediate and intense macrophage reaction with later fibrosis both within lymph vessels and to a lesser extent within lymph nodes. Lymphography indicated that the consequent obstruction resulted more from the effects of silica on vessels than on nodes."

The macrophage reaction within lymph vessels, and the finding that the vessel is the dominant site over the node.

PMID:25401490 SUPPORT Human Clinical

"A moderate lymphoplasmacytic infiltrate was joined by mast cells and scattered macrophages; neutrophils and eosinophils were sparse."

The human counterpart, so this node does not rest on rabbit data alone: the infiltrate in affected human skin is lymphoplasmacytic with mast cells and macrophages, and conspicuously not neutrophilic.

PMID:38448477 SUPPORT INDIRECT Other

"Price also observed that silicate particles caused subendothelial edema, endolymphangitis, collagenisation and obliteration of the lymphatic lumen"

Names subendothelial oedema and endolymphangitis in human tissue, which is this node's exact claim. Graded OTHER and INDIRECT because the sentence is this paper's summary of Price's earlier work rather than its own result.

Lymphatic Vessel Wall Collagenization

Sustained inflammation lays down collagen in and around the lymphatic vessel wall. This is the fibrogenic process; the closed lumen it produces is the next node.

collagen fibril organization GO:0030199 ↑ INCREASED

Downstream

Luminal Obliteration and Loss of Conducting Lymphatics

Show evidence (2 references)

PMID:38448477 SUPPORT INDIRECT Other

"Price also observed that silicate particles caused subendothelial edema, endolymphangitis, collagenisation and obliteration of the lymphatic lumen"

Names collagenisation of the lymphatic wall in sequence with the obliteration it causes, which is the split this pair of nodes represents. Graded OTHER and INDIRECT: the sentence summarises Price's earlier work rather than reporting this paper's own result.

PMID:25401490 SUPPORT Human Clinical

"Dermal collagen bundles were thickened, and elastic fibers were dramatically reduced."

The collagen deposition, measured in affected human skin.

Luminal Obliteration and Loss of Conducting Lymphatics

The end state of the fibrosis: vessels that no longer carry lymph. Biopsy series count fewer lymphatic vessels in affected skin, and a subdermal conducting lymphatic in an affected foot was shown to be fibrosed and impermeable to injected dye - the functional proof, not just the histological one.

Downstream

Lymphatic Obstruction and Lymph Stasis

Show evidence (2 references)

PMID:2604475 SUPPORT Human Clinical

"The conducting lymphatic in the subdermal tissue is found to be impermeable to Patent Blue Violet dye and to be fibrosed."

The functional demonstration that the fibrosed vessel no longer conducts - dye impermeability alongside the histological fibrosis.

PMID:35604949 SUPPORT Human Clinical

"Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as..."

The advanced-stage histopathology, which reports a reduced number of lymphatic vessels alongside the sclerosis.

Lymphatic Obstruction and Lymph Stasis

Lymph cannot leave the limb. The clinical result is swelling that begins at the feet and progressively involves the legs, bilateral in about seven of eight patients, frequently asymmetric between them, and in almost all cases staying below the knee.

lower limb UBERON:0008784

Downstream

Dermal Sclerosis and Nodule Formation

Show evidence (2 references)

PMID:22455414 SUPPORT Human Clinical

"mineral particles in red-clay soils are absorbed through the skin of the foot and engulfed by macrophages in the lower limb lymphatic system, inducing an inflammatory response in the lymphatic vessels, which results in fibrosis and obstruction of the vessel lumen."

Names lymphatic obstruction as the terminal step of the mechanism.

PMID:35604949 SUPPORT Human Clinical

"In 251 (86.9%) patients, both legs were affected by podoconiosis and in 38 (13.1%) only one leg was affected."

The laterality figures behind the "bilateral but not universal" claim, from a 289-patient series.

Dermal Sclerosis and Nodule Formation

Chronic stasis lays down collagen in the dermis, producing thickened sclerotic bundles and the firm nodules of established disease. Nodules are present in about two fifths of patients and are what nodulectomy removes.

collagen fibril organization GO:0030199 ↑ INCREASED

skin of the lower leg and foot UBERON:0001511

Downstream

Epidermal Hyperkeratosis and Barrier Failure

Show evidence (2 references)

PMID:35604949 SUPPORT Human Clinical

"Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as..."

The dermal half of the advanced-stage histopathology - thickening and sclerosis with thickened collagen bundles.

PMID:25401490 SUPPORT Human Clinical

"Dermal collagen bundles were thickened, and elastic fibers were dramatically reduced."

The second biopsy series' account of the same change, adding the elastic fibre loss.

Epidermal Hyperkeratosis and Barrier Failure

The epidermis thickens into verrucous acanthosis and the warty "mossy" plaques the disease is named for, present in about three quarters of patients. Curated separately from the dermal change because it is a different tissue layer and, more importantly, a different claim: this is where the skin stops being a barrier, and it is the node that leads to the acute attacks.

skin of the lower leg and foot UBERON:0001511

Downstream

Acute Dermatolymphangioadenitis Fissured, hyperkeratotic skin is the portal of entry for the skin flora that precipitate the acute attacks.

Show evidence (3 references)

PMID:35604949 SUPPORT Human Clinical

"220 (77.5%) patients had warty lesions, 114 (39.4%) had nodules."

The frequencies of warty lesions and nodules in a 289-patient series.

PMID:35604949 SUPPORT Human Clinical

"Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as..."

The epidermal half of the same histopathology - epidermal thickening and verrucous acanthosis.

PMID:33558538 SUPPORT Human Clinical

"These include dermal nodules and a rough, velvet-like appearance to the skin known as mossy changes which are pathognomonic for the disease."

States that the mossy change is pathognomonic, which is why this node carries diagnostic weight rather than only descriptive weight.

Acute Dermatolymphangioadenitis

Recurrent episodes of fever, pain, erythema and abrupt worsening of the swelling, precipitated by bacteria entering through fissured skin. Each episode damages the lymphatics further, so the entry models it as feeding back into the fibrotic lesion rather than as a terminal complication. It is also the outcome every trial in this disease is powered on, because it is what patients lose working days to.

Downstream

Lymphatic Vessel Wall Collagenization The self-reinforcing loop. Repeated acute inflammation is held to accelerate the underlying fibrosis; the step is described consistently in the clinical literature but has not been dissected, so it is curated with unknown intermediates.

Show evidence (3 references)

PMID:35604949 SUPPORT Human Clinical

"Increased episodes of ADLA were significantly associated with stage 3-5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis."

Ties attack frequency to advanced stage, which is the observation behind the feedback edge - and notes that burning pain instead marks early disease.

PMID:37612446 SUPPORT Human Clinical

"Lymphedema can lead to skin lesions, which can serve as entry points for bacteria that may cause ADLA attacks leading to progression of the lymphedema."

States the skin-breach-to-attack-to-progression sequence, which is the loop this node closes. The source hedges it ("can", "may") and so does this entry: the edge is curated INDIRECT_UNKNOWN_INTERMEDIATES.

PMID:37612446 SUPPORT Human Clinical

"We revealed a positive correlation between increasing lymphedema severity and non-commensal anaerobic bacteria, especially Anaerococcus provencensis, as well as a negative correlation with the presence of Corynebacterium, a constituent of normal skin flora."

Identifies what colonises the affected skin and how it tracks severity - anaerobes up, normal commensal Corynebacterium down. The correlation is with stage, so it does not establish direction on its own.

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Histopathology

3

Verrucous Acanthosis with Thickened Collagen Bundles and Reduced Lymphatic Vessels

The advanced-stage biopsy picture: epidermal and dermal thickening, verrucous acanthosis, a predominantly lymphoplasmacytic infiltrate, dilated and ectatic but fewer lymphatic vessels, eccrine ductal hyperplasia, and sclerotic collagen.

Show evidence (1 reference)

PMID:35604949 SUPPORT Human Clinical

"Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as..."

The full histopathological description this finding records.

Mast Cell and Macrophage Infiltrate with Elastic Fibre Loss

A second biopsy series adds the cellular detail: a moderate lymphoplasmacytic infiltrate joined by mast cells and scattered macrophages, with neutrophils and eosinophils sparse, dramatically reduced elastic fibres, and lymphatics that are reduced in number and mostly not dilated. The cell mix is that of a chronic sterile inflammatory process, not an acute infective one.

Show evidence (2 references)

PMID:25401490 SUPPORT Human Clinical

"All specimens showed verrucous acanthosis and papillomatosis. Eccrine ducts demonstrated hyperplasia, syringofibroadenomatous changes and miliaria. Dermal collagen bundles were thickened, and elastic fibers were dramatically reduced. A moderate lymphoplasmacytic infiltrate was joined by mast..."

The cellular and structural findings this record names, including the sparse neutrophils that argue against an infective picture in the steady state.

PMID:25401490 SUPPORT Human Clinical

"Podoconiosis demonstrates distinctive changes of chronic lymphedema with extensive sclerosis, loss of elastic fibers, verrucous acanthosis (not HPV induced) and reactive changes of eccrine structures."

The authors' summary, which also flags mast cells and macrophages as candidate participants rather than bystanders.

Verrucous Acanthosis Without Human Papillomavirus

The warty, papillomatous surface change is not virally driven. Every specimen tested was HPV-PCR negative, which removes the obvious alternative explanation for a verrucous epidermis and keeps the change attributable to chronic lymphoedema.

Show evidence (1 reference)

PMID:25401490 SUPPORT Human Clinical

"HPV-PCR was negative in all specimens."

Supports this record, which asserts the verrucous change is *not* virally driven; a negative PCR across all specimens is exactly that claim's evidence. Graded SUPPORT rather than REFUTE because `supports` is relative to the record it sits on, not to the hypothesis the result rules out.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

5

Integument 2

Mossy Warty Skin Lesions FREQUENT Hyperkeratosis HP:0000962

Show evidence (2 references)

PMID:35604949 SUPPORT Human Clinical

"220 (77.5%) patients had warty lesions, 114 (39.4%) had nodules."

77.5% carried warty lesions. Tagged FREQUENT rather than VERY_FREQUENT because the figure sits just below the 80% band boundary.

PMID:33558538 SUPPORT Human Clinical

"These include dermal nodules and a rough, velvet-like appearance to the skin known as mossy changes which are pathognomonic for the disease."

States that the mossy appearance is pathognomonic for the disease.

Fibrotic Skin Nodules FREQUENT HP:0200036

Show evidence (1 reference)

PMID:35604949 SUPPORT Human Clinical

"220 (77.5%) patients had warty lesions, 114 (39.4%) had nodules."

39.4% had nodules in the same series - the FREQUENT band.

Metabolism 1

Bilateral Below-Knee Lower-Limb Lymphedema VERY_FREQUENT HP:0001004

Course: PROGRESSIVE

Show evidence (4 references)

PMID:35604949 SUPPORT Human Clinical

"In 251 (86.9%) patients, both legs were affected by podoconiosis and in 38 (13.1%) only one leg was affected."

The laterality split in a 289-patient series - bilateral in 86.9%, which is what the VERY_FREQUENT tag rests on.

PMID:35604949 SUPPORT Human Clinical

"Podoconiosis is a localised disease, primarily starting from the feet, progressively involving the legs, yet in most cases remaining below the knee."

The distribution as the source states it - starting at the feet, progressing up the legs, mostly staying below the knee. Curated in the source's own terms rather than as "ascending", which no cited source says.

PMID:35604949 SUPPORT Human Clinical

"A small number (1.4%) of patients had leg swelling extending above the knee."

The figure behind the below-knee claim.

+ 1 more reference

Musculoskeletal 2

Recurrent Acute Dermatolymphangioadenitis VERY_FREQUENT Cellulitis HP:0100658

Temporal: RECURRENT

Show evidence (5 references)

PMID:35604949 SUPPORT Human Clinical

"Increased episodes of ADLA were significantly associated with stage 3-5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis."

Establishes the stage dependence - attacks concentrate in advanced disease.

PMID:35604949 SUPPORT Human Clinical

"About 86% of the cases in our study had at least one episode of ADLA during the three-month period preceding the date of examination."

The proportion the VERY_FREQUENT tag rests on, and the reason it is this figure rather than any other in the entry: 86% of patients in a 289-patient series restricted to podoconiosis, over a three-month window. That is a patient proportion in a disease-specific cohort, which is what the frequency band is defined on.

PMID:29773516 SUPPORT Human Clinical

"The ratio of incidence rate in the intervention group to that of the control group was 0·81 (0·74 to 0·89; p<0·0001), with a rate difference of -4·5 (-5·1 to -3·8) episodes per person-year."

The episode rate, which is what makes this the outcome trials are powered on. It is a rate per person-year, not a proportion of patients, so it does not by itself set a frequency band.

+ 2 more references

Ankle Ankylosis HP:0031013

Curated without a frequency: the cited series bands its patients as stage 1-2 versus stage 3-5 and does not report how many reach stage 5. It is attached to the lymph-stasis node rather than to the skin node because the fibrosis that fixes the joint is periarticular, and this entry has no periarticular node - the reader should not infer that skin change causes the ankylosis.

Show evidence (1 reference)

PMID:35604949 SUPPORT Human Clinical

"H) Stage 5: fibrotic globular swelling of the left foot and ankle with ankylosis of the ankle joint, multiple areas of scarring (from traditional bloodletting)."

Places ankylosis of the ankle joint in stage 5, quoted from the series' figure legend.

🧬

Genetic Associations

1

HLA class II susceptibility haplotype

Gene: HLA-DQA1 hgnc:4942 relationship_type: SUSCEPTIBILITY variant_origin: GERMLINE

Show evidence (4 references)

PMID:22455414 SUPPORT Human Clinical

"We found a genomewide significant association of podoconiosis with the single-nucleotide polymorphism (SNP) rs17612858, located 5.8 kb from the HLA-DQA1 locus (in the allelic model: odds ratio, 2.44; 95% confidence interval [CI], 1.82 to 3.26; P=1.42×10(-9); and in the additive model: odds..."

The primary genome-wide association result.

PMID:22455414 SUPPORT Human Clinical

"HLA typing showed the alleles HLA-DRB1*0701 (odds ratio, 2.00), DQA1*0201 (odds ratio, 1.91), and DQB1*0202 (odds ratio, 1.79) and the HLA-DRB1*0701-DQB1*0202 haplotype (odds ratio, 1.92) were risk variants for podoconiosis."

The HLA-typed risk alleles and haplotype behind the SNP signal.

PMID:33558538 SUPPORT Human Clinical

"Fourteen SNPs in the HLA class II region showed significant genome-wide association (P < 5.0 × 10-8) with podoconiosis. The lead SNP was rs9270911 (P = 5.51 × 10-10; OR 1.53; 95% CI 1.34-1.74), located near HLA-DRB1."

Replication across three Ethiopian populations, with the lead signal shifting to HLA-DRB1.

+ 1 more reference

💊

Medical Actions

4

Lymphoedema Self-Care Package

Action: Rehabilitation NCIT:C15315

Platform: Behavioral / lifestyle

Foot hygiene, skin care, bandaging, exercise, elevation, and consistent use of socks and shoes, delivered through lay community agents. This is the mainstay and the only management with randomised evidence in this disease. Its measured effect is on acute attacks rather than on limb size, and the effect is real but partial - about a fifth fewer episodes, against a baseline of more than twenty per person-year.

Mechanism Target:

Acute Dermatolymphangioadenitis — Hygiene and emollients close the portals of bacterial entry created by fissured hyperkeratotic skin, which is the step the trial's primary outcome measures.

Show evidence (4 references)

PMID:29773516 SUPPORT Human Clinical

"Patients were randomly assigned (1:1) to either receive a package containing instructions for foot hygiene, skin care, bandaging, exercises, and use of socks and shoes, with support by lay Community Podoconiosis Agents at monthly meetings (intervention group)"

The contents of the package, which is what this treatment describes.

PMID:29773516 SUPPORT Human Clinical

"The ratio of incidence rate in the intervention group to that of the control group was 0·81 (0·74 to 0·89; p<0·0001), with a rate difference of -4·5 (-5·1 to -3·8) episodes per person-year."

The effect estimate. Quoted with the absolute rates attached because the rate ratio alone hides how high the baseline burden is.

PMID:29773516 SUPPORT Human Clinical

"A simple, inexpensive package of lymphoedema self-care is effective in reducing the frequency and duration of acute dermatolymphangioadenitis."

The trial's own conclusion and recommendation.

+ 1 more reference

Nodulectomy

Action: Surgical Procedure NCIT:C15329

Platform: Surgery

Surgical excision of woody fibrotic nodules under local anaesthesia, wounds left to heal by secondary intention under compression. Reserved for nodules that do not respond to conservative care. It improves quality of life and, unexpectedly for a debulking procedure, reduces acute attack frequency.

Mechanism Target:

Dermal Sclerosis and Nodule Formation — The procedure removes the fibrotic nodules this node produces; it does not address the lymphatic obstruction upstream of them.

Show evidence (3 references)

PMID:33481805 SUPPORT Human Clinical

"The DLQI values were significantly better six months after surgery than before surgery (P<0.0001)."

The quality-of-life outcome at six months.

PMID:33481805 SUPPORT Human Clinical

"Also the number of ADLA episodes per three months was significantly lower six months after surgery than before surgery (P<0.0001)."

The acute-attack reduction, which is the more surprising result: removing nodules also removed some of the infection risk.

PMID:33481805 SUPPORT Human Clinical

"Excisions after nodulectomy were left to heal by secondary intention with compression bandaging."

The wound-management detail that makes this a resource-appropriate procedure rather than one requiring a theatre and grafting.

Antibiotic Therapy for Acute Attacks

Action: Pharmacotherapy NCIT:C15986

Platform: Small molecule

Antibiotics, penicillin among them, are the recommended treatment for interrupting an acute dermatolymphangioadenitis episode. Curated with the qualifier the source attaches to it and that this entry will not drop: in the remote rural populations where the disease actually occurs, they are not routinely available. The recommendation and its reach are different claims.

Mechanism Target:

Acute Dermatolymphangioadenitis — Antibiotics act on the bacterial arm of the acute episode, not on the lymphatic obstruction that produced the portal of entry.

Show evidence (1 reference)

PMID:29773516 SUPPORT Other

"Antibiotic therapy (including penicillin), which has been recommended for interruption of acute dermatolymphangioadenitis episodes,17 is not routinely available for patients in remote rural populations in Ethiopia."

Carries both halves of the claim in one sentence - the recommendation and the availability caveat. Graded OTHER: the sentence is this trial's background framing, citing an earlier recommendation, not a result of the trial itself. No trial of antibiotic therapy in podoconiosis is cited in this entry.

Consistent Footwear Use

Action: consistent footwear use to interrupt soil contact Ontology label: Preventive Intervention NCIT:C15843

Platform: Behavioral / lifestyle

Shoes are the primary prevention, and in early-stage disease they are also treatment. Because the exposure is transdermal and the early lymphoedema is reversible, interrupting soil contact can halt or reverse stage 1-2 disease. This is the intervention that makes podoconiosis eliminable in a way its fellow lymphoedemas are not.

Mechanism Target:

Chronic Barefoot Contact with Alkalic Volcanic Clay Soil — Footwear acts on the exposure itself rather than on any downstream mechanism, which is why it can prevent as well as treat.

Show evidence (3 references)

PMID:40898820 SUPPORT Other

"Early intervention, including consistent use of footwear and improved foot hygiene, can greatly reduce disease burden."

States the effect of footwear and hygiene on disease burden. Graded OTHER because it is a review's summary statement rather than a measured result.

PMID:35604949 SUPPORT Human Clinical

"In stages 1 and 2, simple lymphoedema management can completely reverse the clinical changes, but if the condition is not managed with appropriate foot care and consistent shoe wearing, it can lead to subsequent ir"

The reversibility claim this treatment rests on, stated for stages 1 and 2 and tied to consistent shoe wearing. Without it the description's "halt or reverse" would be asserting more than the footwear evidence shows.

PMID:37719165 SUPPORT INDIRECT Human Clinical

"Walking barefoot adjusted odd ratio (AOR) 5.35 (95% CI: 1.65, 9.05), p = 0.001, not washing feet with soap and water regularly AOR 2.8 (95% CI: 1.16, 4.44, p = 0.001), and an increased age AOR 2.23 (95% CI: 1.25, 5.58) were factors significantly associated with the prevalence of podoconiosis."

Graded INDIRECT: the odds ratio is for walking barefoot as a risk factor, so the protective effect of footwear follows by inversion rather than being measured directly. No randomised trial of footwear exists.

🌍

Environmental Factors

1

Long-term barefoot contact with red-clay soil derived from alkalic volcanic rock

Hazard type: CHEMICAL

Route: DERMAL

Duration: CHRONIC

Exposome domain: SPECIFIC EXTERNAL

No IARC group is recorded. IARC has not classified this soil exposure, and podoconiosis is not a neoplastic outcome. No GHS class is recorded either: the exposure is a natural soil rather than a classified substance.

The necessary environmental cause. Exposure is transdermal rather than inhalational, occurs over years of subsistence farming without footwear, and is determined by soil geochemistry - endemic areas sit on alkalic volcanic bedrock at high altitude with high rainfall, the conditions that weather it into the implicated clays.

Show evidence (3 references)

PMID:22455414 SUPPORT Human Clinical

"Podoconiosis is a tropical lymphedema resulting from long-term barefoot exposure to red-clay soil derived from volcanic rock. The World Health Organization recently designated it as a neglected tropical disease. Podoconiosis develops in only a subgroup of exposed people, and studies have shown..."

The canonical statement of the exposure and its duration.

PMID:40623043 SUPPORT Human Clinical

"Nine studies found a correlation between podoconiosis occurrence and regions with underlying alkalic volcanic bedrock, and six linked pedogenic factors (altitude and rainfall) with disease occurrence. Several studies linked specific soil mineralogy and geochemistry with endemic regions,..."

The bedrock, pedogenic and mineralogical correlates that make this a geochemically defined exposure rather than a geographic one.

PMID:40623043 SUPPORT Human Clinical

"However, it remains unclear whether these are covariates or direct contributors to the pathogenesis of the disease"

The systematic review's own caution that the mineral correlations may be covariates rather than causes. Curated because this entry names specific minerals and should not imply more than the source does.

Mechanism Target:

TRIGGERS Transdermal Entry of Silicate Mineral Particles — Barefoot soil contact is the route by which the mineral particles reach the skin at all; there is no other described exposure pathway.

Show evidence (1 reference)

PMID:40898820 SUPPORT Other

"It arises due to prolonged exposure of bare feet to irritant red-clay soils in genetically susceptible individuals."

States the exposure and the susceptibility requirement together, which is exactly what this edge and its downstream HLA node jointly assert. Graded OTHER: the source is a narrative review and the sentence is its own summary statement, not a reported result.

🔬

Diagnosis

1

Clinical Diagnosis with Exclusion of Lymphatic Filariasis

There is no confirmatory test. Diagnosis rests on the exposure history, the bilateral below-knee distribution and the mossy skin change, with a negative filarial antigen test to exclude the principal mimic. The HLA association is a research finding and is not a diagnostic test.

Show evidence (2 references)

PMID:35604949 SUPPORT Human Clinical

"Dermatologists performed a patient history, physical examination, filariasis test strip, and skin biopsy for histopathologic examination."

The assessment sequence used in a large field series, including the filariasis test strip that does the excluding.

PMID:33558538 SUPPORT Human Clinical

"These include dermal nodules and a rough, velvet-like appearance to the skin known as mossy changes which are pathognomonic for the disease."

The pathognomonic sign that carries the positive half of the diagnosis once filariasis is excluded.

📈

Progression

2

Reversible Early Disease

Stages 1-2. Swelling is soft and pitting and still responds to elevation, footwear and hygiene. About three fifths of patients in a community series were in this band, which is where the prevention argument has its purchase.

Show evidence (1 reference)

PMID:35604949 SUPPORT Human Clinical

"We recruited 289 patients for the study, 178 (61.6%) had stage 1 or 2 podoconiosis, and 111(38.4%) stage 3 to 5 podoconiosis."

The stage distribution this phase describes.

Fixed Fibrotic Disease

Stages 3-5. Non-pitting oedema, established dermal sclerosis, nodules and eventually ankylosis. Acute attacks become more frequent as the stage advances, so the fibrotic phase is also the phase with the highest acute burden. Self-care still helps here; reversal does not.

Show evidence (2 references)

PMID:35604949 SUPPORT Human Clinical

"Increased episodes of ADLA were significantly associated with stage 3-5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis."

The association between advanced stage and acute-attack frequency that makes this phase clinically distinct.

PMID:35604949 SUPPORT Human Clinical

"Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as..."

The histological correlates of the fixed phase.

🪜

Stages

5

Stage 1

Early and reversible. Burning pain in the feet, splaying of the forefoot, accentuated skin markings over the metatarsophalangeal joints.

Show evidence (2 references)

PMID:35604949 SUPPORT Human Clinical

"B) Stage 1: splaying of the right forefoot, accentuation of the skin markings on the metatarsophalangeal joint."

The clinical description of this stage, from the series' own figure legend.

PMID:35604949 SUPPORT Human Clinical

"Increased episodes of ADLA were significantly associated with stage 3-5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis."

Places burning pain in the early stages, which is the symptom this stage is recognised by.

Stage 2

Bilateral lymphoedema below the knee, still soft, with warty hyperkeratotic papules beginning to cover the dorsum of the feet.

Show evidence (1 reference)

PMID:35604949 SUPPORT Human Clinical

"C) Stage 2: bilateral lymphoedema below the knee."

The stage description from the series' figure legend.

Stage 3

Fibrotic, non-pitting oedema below the knee, with early nodules and skin changes. The transition from stage 2 to stage 3 is where reversibility is lost.

Curated without its own evidence item. The cached source illustrates stages 1, 2, 4 and 5 in its figure legends but not stage 3 separately; the description follows the five-stage system the source cites rather than a quotable sentence, and is flagged here rather than given a snippet that does not say it.

Stage 4

Non-pitting oedematous swelling extending above the knee, with skin depigmentation around the ankle. Reached by only a small minority.

Show evidence (2 references)

PMID:35604949 SUPPORT Human Clinical

"G) Stage 4 (right) and stage 2 (left). Right foot: non pitting oedematous swelling of the leg extending above the knee with an area of skin depigmentation around the ankle."

The stage description, and incidentally a demonstration that the two legs can sit at different stages in one patient.

PMID:35604949 SUPPORT Human Clinical

"A small number (1.4%) of patients had leg swelling extending above the knee."

How rarely this stage is reached - 1.4% of the series had swelling above the knee at all.

Stage 5

Fixed, globular, woody swelling with ankylosis of the ankle joint, multiple nodules and band-like redundant skin folds.

Show evidence (2 references)

PMID:35604949 SUPPORT Human Clinical

"H) Stage 5: fibrotic globular swelling of the left foot and ankle with ankylosis of the ankle joint, multiple areas of scarring (from traditional bloodletting)."

The stage description, which is also the source of the ankylosis phenotype's evidence.

PMID:35604949 SUPPORT Human Clinical

"We recruited 289 patients for the study, 178 (61.6%) had stage 1 or 2 podoconiosis, and 111(38.4%) stage 3 to 5 podoconiosis."

The distribution across the two stage bands in a community series - about three fifths early, two fifths advanced.

📊

Prevalence

2

Sub-Saharan Africa

Point Prevalence 2660.0 per 100,000 (2240.0–3100.0) >1 in 1,000

Pooled across 16 studies and 2,195,722 individuals. Heterogeneity is extreme (I-squared 99.9%), which is expected for a disease whose distribution is set by local bedrock - the pooled figure describes the region, not any district in it.

Show evidence (1 reference)

PMID:37719165 SUPPORT Human Clinical

"The pooled prevalence of podoconiosis was 2.66 (95% confidence interval (CI): 2.24, 3.10) with heterogeneity index (I2) of 99.9%."

The pooled estimate and its confidence interval and heterogeneity index.

Worldwide

Cases In Literature Rare

About four million people affected globally, concentrated in tropical highland regions. Recorded as a case count rather than a rate because the source gives an absolute burden without a denominator.

Show evidence (1 reference)

PMID:33558538 SUPPORT Human Clinical

"It is estimated that there are 4 million people living with podoconiosis globally, mainly living in highland regions of tropical countries in Africa, South and Central America and southeast Asia"

The global burden estimate and its geographic distribution.

🌍

Epidemiology

1

Exposure-Dependent Distribution Set by Bedrock and Climate

The disease occurs where alkalic volcanic bedrock weathers under high altitude and high rainfall into the implicated clays, and where people farm that soil barefoot. Both conditions are required, which is why podoconiosis is absent from equally volcanic areas where footwear is universal.

Show evidence (2 references)

PMID:40623043 SUPPORT Human Clinical

"Nine studies found a correlation between podoconiosis occurrence and regions with underlying alkalic volcanic bedrock, and six linked pedogenic factors (altitude and rainfall) with disease occurrence. Several studies linked specific soil mineralogy and geochemistry with endemic regions,..."

The bedrock and pedogenic correlations behind the distribution.

PMID:37719165 SUPPORT Human Clinical

"Walking barefoot adjusted odd ratio (AOR) 5.35 (95% CI: 1.65, 9.05), p = 0.001, not washing feet with soap and water regularly AOR 2.8 (95% CI: 1.16, 4.44, p = 0.001), and an increased age AOR 2.23 (95% CI: 1.25, 5.58) were factors significantly associated with the prevalence of podoconiosis."

The behavioural half of the requirement, with foot hygiene and age alongside it.

🔀

Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from Podoconiosis:

Lymphatic Filariasis

Overlapping Features The principal differential and the reason a filarial antigen test is part of every case definition. The distinction this entry curates is mechanistic rather than a bedside rule of thumb: in filariasis the lymphatic disruption is proximal, at worm nests in the groin or armpits, whereas in podoconiosis the insult enters at the feet and the disease stays localised to the legs. The two are co-endemic in a number of countries, so geography does not settle it either.

Show evidence (4 references)

PMID:35604949 SUPPORT Human Clinical

"Dermatologists performed a patient history, physical examination, filariasis test strip, and skin biopsy for histopathologic examination."

Shows the exclusion being performed in practice - the test strip is part of the standard workup, not an optional extra.

PMID:33348721 SUPPORT Other

"Whereas the lymphatic disruption in LF is proximal (worm nests in the groin or armpits), in podoconiosis the exposure is at the feet"

The mechanistic contrast this record now rests on - proximal worm nests versus distal soil entry. Graded OTHER: the sentence is the paper's framing of the two diseases rather than a result of its trial.

PMID:35604949 SUPPORT Human Clinical

"Podoconiosis is a localised disease, primarily starting from the feet, progressively involving the legs, yet in most cases remaining below the knee."

The localisation half of the contrast, in the source's own words. An earlier draft of this record asserted an "ascending" versus "descending" distinction and groin sparing; no cited source says any of that, and it has been replaced with what the sources do say.

+ 1 more reference

🔬

Clinical Trials

2

ISRCTN67805210 NOT_APPLICABLE COMPLETED

GoLBeT, the Gojjam Lymphoedema Best Practice Trial: a pragmatic single-blind randomised controlled trial of a community-delivered lymphoedema self-care package in northern Ethiopia, powered on acute dermatolymphangioadenitis episodes. Results published as PMID:29773516.

Target Phenotypes: recurrent acute dermatolymphangioadenitis HP:0100658

Show evidence (1 reference)

ICTRP:ISRCTN67805210 SUPPORT Other

"| Study design | Pragmatic single-blind randomized controlled trial (Treatment) |"

The registry record establishing the trial's design. Graded OTHER because a registration document is not itself study evidence; the results are curated on the Lymphoedema Self-Care Package treatment.

ISRCTN16764792 NOT_APPLICABLE COMPLETED

Enhanced self-care for advanced lymphoedema: a comparative study in Ethiopia and Bangladesh testing whether adding lymphatic stimulation - self-massage and deep breathing - to the standard hygiene package improves outcomes. Results published as PMID:33348721.

Show evidence (1 reference)

ICTRP:ISRCTN16764792 SUPPORT Other

"| Countries of recruitment | Bangladesh; Ethiopia |"

The registry record. Listed because the trial's published results are curated on the self-care treatment and the identifier should be machine-findable rather than sitting in prose.

🐁

Animal Models

1

Intralymphatic silica injection model

Fine silica particles injected directly into lymphatic vessels, designed to test whether the mineral alone can produce the obstructive lesion and to locate its main site of action. It bypasses the skin and the adaptive immune system entirely, which is both its power and its limit. The species is taken from the record's MeSH indexing (Rabbits); the abstract itself says only "animal experiments".

Species

Rabbit

Genotype

Wild type

Publication

PMID:3006293

Pathograph links

Endolymphangitis partially recapitulates fidelity: moderate observes: tissue Silica provoked immediate intense macrophage reaction and later fibrosis within lymph vessels, with lymphographic obstruction attributable more to the vessels than to the nodes.

Limitations: Direct intralymphatic injection is not the human exposure route: it skips transdermal entry, delivers a bolus rather than a decades-long trickle, and uses silica rather than the kaolinite that predominates in human lymph node microanalysis. It also cannot model the HLA class II susceptibility, since the animals are not selected for it - so the model shows the mineral is sufficient for the vessel lesion in an unselected host, which is a different claim from the human one.

Divergences from the human mechanism

boundary omission qualifying

The plantar skin barrier and the whole transdermal entry step are outside the model. Everything this entry curates upstream of the lymphatic is untested by it.

proxy quantity qualifying

The injected material is fine silica; the quantity the human node concerns is chronic kaolinite-dominant silicate deposition arriving via macrophage transport. Same mineral class, different species and different delivery.

population mismatch invalidating

Human disease occurs in the subset of exposed people carrying HLA class II risk haplotypes. The experimental animals are unselected, so the model cannot speak to the susceptibility step that decides who gets the disease.

Show evidence (1 reference)

PMID:3006293 SUPPORT Model Organism

"Intralymphatic silica provoked an immediate and intense macrophage reaction with later fibrosis both within lymph vessels and to a lesser extent within lymph nodes. Lymphography indicated that the consequent obstruction resulted more from the effects of silica on vessels than on nodes."

The experimental result, including the vessel-over-node localisation that this entry's chain follows.

{ }

Source YAML

click to show

name: Podoconiosis
creation_date: "2026-09-07T00:00:00Z"
category: Environmental Lymphatic Disease
parents:
- Lymphedema
- Neglected Tropical Disease
disease_term:
  preferred_term: podoconiosis
  term:
    id: MONDO:0005425
    label: podoconiosis
synonyms:
- Endemic non-filarial elephantiasis
- Mossy foot
- Geochemical elephantiasis
description: >-
  Podoconiosis is a non-infectious lymphoedema of the lower legs caused by years
  of barefoot contact with red-clay soil derived from alkalic volcanic rock. It
  is the clearest gene-environment disease among the neglected tropical
  diseases: there is no pathogen and no vector, the exposure is a mineral, and
  the susceptibility is an HLA class II haplotype. Endemic soils carry
  kaolinite, smectite, quartz, iron oxides and trace beryllium and zirconium;
  kaolinite is the species actually identified in human lymph node tissue, and
  which of them is the trigger is unknown. Colloid-sized silicate particles
  cross the plantar skin, are taken up by dermal macrophages, and reach the
  lower-limb lymphatics. In people carrying the risk haplotypes
  this is followed by a sustained inflammatory response - read as CD4
  T-cell-mediated from the class II association, though no antigen-specific
  response has been demonstrated - that collagenizes and obliterates the
  lymphatic lumen. The swelling starts at the feet, is bilateral in about seven
  of eight patients, is often asymmetric between the legs, and in almost all
  cases stays below the knee. The skin thickens into the warty, nodular "mossy"
  changes the disease is named
  for it, and recurrent bacterial acute dermatolymphangioadenitis drives further
  lymphatic damage in a self-reinforcing loop. Roughly four million people are
  affected across some 32 countries, about a quarter of them in Ethiopia. The
  disease is entirely preventable with shoes, and its early stages are
  reversible; established fibrosis is not.
pathophysiology:
- name: Chronic Barefoot Contact with Alkalic Volcanic Clay Soil
  description: >-
    The necessary exposure. Subsistence farmers working barefoot on red clay
    weathered from alkalic volcanic bedrock accumulate contact over years to
    decades. The soil is the operative agent, not the terrain: endemicity tracks
    bedrock geochemistry and the pedogenic conditions that produce these clays -
    high altitude and high rainfall - rather than any vector distribution.
  biological_scale: ORGANISM
  downstream:
  - target: Transdermal Entry of Silicate Mineral Particles
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Podoconiosis is a tropical lymphedema resulting from long-term barefoot exposure to red-clay soil derived from volcanic rock. The World Health Organization recently designated it as a neglected tropical disease. Podoconiosis develops in only a subgroup of exposed people, and studies have shown familial clustering with high heritability (63%)."
    explanation: >-
      States the exposure and its duration, which is what this node records, and
      the heritability figure that makes the exposure necessary rather than
      sufficient.
  - reference: PMID:40623043
    reference_title: "Associations between podoconiosis and pedogenic factors globally - A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nine studies found a correlation between podoconiosis occurrence and regions with underlying alkalic volcanic bedrock, and six linked pedogenic factors (altitude and rainfall) with disease occurrence. Several studies linked specific soil mineralogy and geochemistry with endemic regions, including an abundance of phyllosilicate clay minerals, quartz, and trace elements, notably iron, beryllium and zirconium."
    explanation: >-
      The systematic review's bedrock and pedogenic correlations, and the
      mineral inventory that the next node's particles come from.
  - reference: PMID:37719165
    reference_title: "Epidemiology of podoconiosis in sub-Saharan Africa: A systematic review and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Walking barefoot adjusted odd ratio (AOR) 5.35 (95% CI: 1.65, 9.05), p = 0.001, not washing feet with soap and water regularly AOR 2.8 (95% CI: 1.16, 4.44, p = 0.001), and an increased age AOR 2.23 (95% CI: 1.25, 5.58) were factors significantly associated with the prevalence of podoconiosis."
    explanation: >-
      The effect estimate for the behaviour itself - walking barefoot carries an
      adjusted odds ratio above five in pooled sub-Saharan data.

- name: Transdermal Entry of Silicate Mineral Particles
  description: >-
    Colloid-sized silicate particles cross the plantar and dorsal skin of the
    foot and lodge in the dermis. Their identity is partly known and partly not:
    kaolinite predominates in lymph node microanalysis at 0.2-2 micrometres, and
    endemic soils are enriched in smectite, mica, quartz, iron oxides, beryllium
    and zirconium - but which constituent is the operative trigger has never
    been established.
  biological_scale: TISSUE
  locations:
  - preferred_term: dermis of the foot
    term:
      id: UBERON:0002067
      label: dermis
  downstream:
  - target: Macrophage Phagocytosis of Mineral Particles
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:2604475
      reference_title: "Soil particles in the tissues of the foot in endemic elephantiasis of the lower legs."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The presence of microparticles of clay is demonstrated in the dermis of the foot in a patient with endemic elephantiasis. The particles are seen to be in the phagosomes of macrophages or in the cytoplasm of other cells."
      explanation: >-
        Shows the particles already inside macrophage phagosomes in the foot
        dermis, which is the step this edge asserts.
  evidence:
  - reference: PMID:2604475
    reference_title: "Soil particles in the tissues of the foot in endemic elephantiasis of the lower legs."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presence of microparticles of clay is demonstrated in the dermis of the foot in a patient with endemic elephantiasis. The particles are seen to be in the phagosomes of macrophages or in the cytoplasm of other cells."
    explanation: >-
      The direct demonstration that clay microparticles are present in the
      dermal tissue of an affected foot.
  - reference: PMID:39591258
    reference_title: "Differences in Cytokine Expression at Baseline and in Response to Mineral Stimulation by Peripheral Blood Mononuclear Cells from Podoconiosis Cases and Healthy Control Individuals."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The predominant silica particles were mainly of the kaolinite type, sized between 0.2 and 2 µm"
    explanation: >-
      Gives the dominant mineral species and its size range, which is what makes
      transdermal entry mechanically plausible. Graded OTHER because the
      sentence is this paper's summary of the earlier microanalysis literature,
      not its own measurement.

- name: Macrophage Phagocytosis of Mineral Particles
  description: >-
    Dermal macrophages engulf the silicate particles. This step is not itself
    pathological - particles are found in the lymph nodes of unaffected
    residents of endemic areas too, which is why the entry treats deposition as
    necessary and the host response as what separates disease from exposure.
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: dermal macrophage
    term:
      id: CL:0000235
      label: macrophage
  biological_processes:
  - preferred_term: phagocytosis
    modifier: INCREASED
    term:
      id: GO:0006909
      label: phagocytosis
  locations:
  - preferred_term: dermis of the foot
    term:
      id: UBERON:0002067
      label: dermis
  downstream:
  - target: Lymphatic Transport of Particle-Laden Macrophages
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:2604475
    reference_title: "Soil particles in the tissues of the foot in endemic elephantiasis of the lower legs."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presence of microparticles of clay is demonstrated in the dermis of the foot in a patient with endemic elephantiasis. The particles are seen to be in the phagosomes of macrophages or in the cytoplasm of other cells."
    explanation: >-
      The particles inside macrophage phagosomes, which is precisely this node's
      claim.
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The disease develops in only some people exposed to irritant soils, although mineral particles can be seen in the lymphatic system and lymph nodes of unaffected as well as affected people."
    explanation: >-
      The observation that makes this node insufficient on its own: particles
      are present in unaffected people too. Curated here because it is the
      reason the HLA node exists.

- name: Lymphatic Transport of Particle-Laden Macrophages
  description: >-
    Particle-laden macrophages migrate into the lower-limb lymphatic vessels and
    on to the regional lymph nodes, where the silicates are recoverable by
    microanalysis. From here the chain forks: one arm needs the HLA class II
    susceptibility, the other does not.
  biological_scale: CELLULAR
  locations:
  - preferred_term: lower-limb lymphatic vessel
    term:
      id: UBERON:0001473
      label: lymphatic vessel
  downstream:
  - target: HLA Class II-Restricted CD4 T-Cell Response
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      How a mineral particle comes to be presented on an HLA class II molecule
      is the central unsolved step in this disease, so the edge is curated with
      unknown intermediates rather than asserted as antigen presentation.
  - target: Endolymphangitis
    causal_link_type: DIRECT
    description: >-
      Silica delivered directly into a lymphatic provokes macrophage reaction
      and fibrosis in the vessel wall without requiring the adaptive arm, which
      is the second, HLA-independent route to the same lesion.
    evidence:
    - reference: PMID:3006293
      reference_title: "The effects of silica on lymph nodes and vessels--a possible mechanism in the pathogenesis of non-filarial endemic elephantiasis."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Intralymphatic silica provoked an immediate and intense macrophage reaction with later fibrosis both within lymph vessels and to a lesser extent within lymph nodes. Lymphography indicated that the consequent obstruction resulted more from the effects of silica on vessels than on nodes."
      explanation: >-
        The intralymphatic injection experiment, which establishes that the
        particles alone can produce the vessel lesion and locates the effect in
        vessels rather than nodes.
  evidence:
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "mineral particles in red-clay soils are absorbed through the skin of the foot and engulfed by macrophages in the lower limb lymphatic system, inducing an inflammatory response in the lymphatic vessels, which results in fibrosis and obstruction of the vessel lumen."
    explanation: >-
      States the transport-to-lymphatics model this node represents, and names
      the inflammatory consequence the downstream nodes carry.
  - reference: PMID:39591258
    reference_title: "Differences in Cytokine Expression at Baseline and in Response to Mineral Stimulation by Peripheral Blood Mononuclear Cells from Podoconiosis Cases and Healthy Control Individuals."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Silicate particles of the kaolinite and aluminum types have been identified in femoral lymph node biopsy samples from endemic area residents, suggesting a possible role in the pathogenesis of podoconiosis."
    explanation: >-
      Locates the particles in femoral lymph node biopsies, the endpoint of the
      transport this node describes. Graded OTHER: background prose citing the
      earlier microanalysis literature, not this study's own result.

- name: HLA Class II-Restricted CD4 T-Cell Response
  description: >-
    The susceptibility step. Genome-wide association in Ethiopian populations
    places the signal squarely in the HLA class II region, replicated across
    three ethnic groups and with no other locus reaching significance in a
    better-powered second study. A class II association in a non-communicable
    disease is read as a CD4 T-cell-mediated response - but the antigen itself
    is unidentified, and whether the mineral is presented, modifies a self
    peptide, or binds the groove directly is unknown. Berylliosis is the
    explicit comparator.
  biological_scale: CELLULAR
  genes:
  - preferred_term: HLA-DQA1
    term:
      id: hgnc:4942
      label: HLA-DQA1
  - preferred_term: HLA-DRB1
    term:
      id: hgnc:4948
      label: HLA-DRB1
  - preferred_term: HLA-DQB1
    term:
      id: hgnc:4944
      label: HLA-DQB1
  cell_types:
  - preferred_term: CD4-positive T cell
    term:
      id: CL:0000624
      label: CD4-positive, alpha-beta T cell
  biological_processes:
  - preferred_term: antigen processing and presentation via MHC class II
    modifier: INCREASED
    term:
      id: GO:0019886
      label: antigen processing and presentation of exogenous peptide antigen via MHC class II
  downstream:
  - target: Chronic Systemic Immune Activation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found a genomewide significant association of podoconiosis with the single-nucleotide polymorphism (SNP) rs17612858, located 5.8 kb from the HLA-DQA1 locus (in the allelic model: odds ratio, 2.44; 95% confidence interval [CI], 1.82 to 3.26; P=1.42×10(-9); and in the additive model: odds ratio, 2.19; 95% CI, 1.66 to 2.90; P=3.44×10(-8))"
    explanation: The genome-wide significant signal that anchors this node, with its effect size.
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HLA typing showed the alleles HLA-DRB1*0701 (odds ratio, 2.00), DQA1*0201 (odds ratio, 1.91), and DQB1*0202 (odds ratio, 1.79) and the HLA-DRB1*0701-DQB1*0202 haplotype (odds ratio, 1.92) were risk variants for podoconiosis."
    explanation: >-
      The classical HLA typing behind the SNP association, naming the risk
      alleles and the haplotype.
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Association between variants in HLA class II loci with podoconiosis (a noncommunicable disease) suggests that the condition may be a T-cell-mediated inflammatory disease and is a model for gene-environment interactions that may be relevant to other complex genetic disorders."
    explanation: >-
      Graded INDIRECT because the T-cell interpretation follows from the class
      II association by inference; the authors state it as a suggestion, and no
      antigen-specific T-cell response has been demonstrated.
  - reference: PMID:33558538
    reference_title: "Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fourteen SNPs in the HLA class II region showed significant genome-wide association (P < 5.0 × 10-8) with podoconiosis. The lead SNP was rs9270911 (P = 5.51 × 10-10; OR 1.53; 95% CI 1.34-1.74), located near HLA-DRB1."
    explanation: >-
      The replication in a larger, three-population sample, with its own lead
      SNP near HLA-DRB1.
  - reference: PMID:33558538
    reference_title: "Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings confirm the HLA class II association with podoconiosis suggesting HLA-mediated abnormal induction and regulation of immune responses may have a direct role in its pathogenesis."
    explanation: >-
      The replication study's own reading of what the association implies, again
      hedged - "may have a direct role" - which is the strength this node claims.
  - reference: PMID:33099652
    reference_title: "Multiplexed gene expression analysis of HLA class II-associated podoconiosis implicates chronic immune activation in its pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Gene ontology analysis showed differentially expressed genes to be closely related to major histocompatibility complex protein, cytokine and TNF receptor binding genes. Pathway enrichment analysis revealed involvement of lymphocyte activation, adaptive immunity, cytokine signalling, antigen processing and the IL-12 pathways."
    explanation: >-
      The functional bridge from the genetic association to a mechanism: the
      differentially expressed genes in affected lymph node tissue enrich for
      MHC protein and antigen processing, which is what a class II association
      predicts and had not previously been shown.
  - reference: PMID:33099652
    reference_title: "Multiplexed gene expression analysis of HLA class II-associated podoconiosis implicates chronic immune activation in its pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "NanoString technology was used to assess expression of 579 immune-related genes in formalin-fixed and paraffin-embedded lymph node archival samples from podoconiosis patients and unaffected controls."
    explanation: >-
      Records that the measurement was made in lymph node tissue rather than
      blood, which is what makes it evidence about the lesion site.

- name: Chronic Systemic Immune Activation
  description: >-
    Patients carry a measurably activated immune system at rest: raised HLA-DR
    on circulating CD4 and CD8 T cells, raised CD40 and CD86 on monocytes and
    dendritic cells, lower CD62L, and higher unstimulated TNF-alpha and
    IL-1beta than endemic controls. The activation is systemic, not confined to
    the affected limb.
  biological_scale: ORGANISM
  cell_types:
  - preferred_term: monocyte
    term:
      id: CL:0000576
      label: monocyte
  - preferred_term: dendritic cell
    term:
      id: CL:0000451
      label: dendritic cell
  biological_processes:
  - preferred_term: inflammatory response
    modifier: INCREASED
    term:
      id: GO:0006954
      label: inflammatory response
  downstream:
  - target: Endolymphangitis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The systemic activation is measured in blood and the lesion is in the
      limb lymphatics; no study connects the two directly, so the edge is
      curated with unknown intermediates. The direction is assumed, not shown:
      every cited measurement is cross-sectional case-control, and systemic
      activation is at least as plausibly a consequence of chronic lesional
      inflammation and recurrent acute attacks as a cause of them.
  evidence:
  - reference: PMID:38448477
    reference_title: "Evidence for immune activation in pathogenesis of the HLA class II associated disease, podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Peripheral blood immunophenotyping of T cells indicated podoconiosis patients had significantly higher CD4 and CD8 T cell surface HLA-DR expression compared to healthy controls while CD62L expression was significantly lower."
    explanation: The T-cell activation phenotype this node records, against endemic healthy controls.
  - reference: PMID:38448477
    reference_title: "Evidence for immune activation in pathogenesis of the HLA class II associated disease, podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The levels of the activation markers CD40 and CD86 were significantly higher on monocytes and dendritic cell subsets in patients compared to the controls."
    explanation: The antigen-presenting-cell arm of the same activation state.
  - reference: PMID:38448477
    reference_title: "Evidence for immune activation in pathogenesis of the HLA class II associated disease, podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our finding provides evidence that podoconiosis is associated with high levels of immune activation and inflammation with over-expression of genes within the pro-inflammatory axis."
    explanation: The study's summary claim, which is what this node asserts.
  - reference: PMID:39591258
    reference_title: "Differences in Cytokine Expression at Baseline and in Response to Mineral Stimulation by Peripheral Blood Mononuclear Cells from Podoconiosis Cases and Healthy Control Individuals."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Our results showed that the levels of TNF-α and IL-1β from in vitro cell cultures were significantly higher in unstimulated samples from patients compared to controls (p = 0.04 and p = 0.005, respectively)."
    explanation: >-
      The baseline cytokine difference, measured without stimulation, which is
      the "at rest" part of this node's claim.
  - reference: PMID:39591258
    reference_title: "Differences in Cytokine Expression at Baseline and in Response to Mineral Stimulation by Peripheral Blood Mononuclear Cells from Podoconiosis Cases and Healthy Control Individuals."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The minerals kaolinite and chlorite induced two and three-fold higher levels of IL-1β following 24 h of stimulation in healthy controls compared to patients, respectively."
    explanation: >-
      Counterintuitive and load-bearing. On stimulation with kaolinite and
      chlorite it was the healthy endemic controls, not the patients, who
      produced more IL-1beta - the opposite of what a hypersensitivity model
      predicts. It is graded SUPPORT because it supports *this* node's claim, a
      chronically activated or exhausted immune state, rather than the
      hypersensitivity reading; `supports` is relative to the record it sits on,
      and no node in this entry asserts hypersensitivity for it to refute. The
      argument is carried in the `podo_inverted_mineral_response` discussion.

- name: Endolymphangitis
  description: >-
    Inflammation of the lymphatic vessel wall, with subendothelial oedema and a
    lymphoplasmacytic infiltrate. This is the lesion the two upstream arms - the
    HLA-restricted response and the direct particle effect - converge on.
  biological_scale: TISSUE
  cell_types:
  - preferred_term: lymphatic vessel endothelial cell
    term:
      id: CL:0002138
      label: endothelial cell of lymphatic vessel
  locations:
  - preferred_term: lymphatic vessel of the lower limb
    term:
      id: UBERON:0001473
      label: lymphatic vessel
  downstream:
  - target: Lymphatic Vessel Wall Collagenization
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:3006293
    reference_title: "The effects of silica on lymph nodes and vessels--a possible mechanism in the pathogenesis of non-filarial endemic elephantiasis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Intralymphatic silica provoked an immediate and intense macrophage reaction with later fibrosis both within lymph vessels and to a lesser extent within lymph nodes. Lymphography indicated that the consequent obstruction resulted more from the effects of silica on vessels than on nodes."
    explanation: >-
      The macrophage reaction within lymph vessels, and the finding that the
      vessel is the dominant site over the node.
  - reference: PMID:25401490
    reference_title: "Histopathological and immunohistochemical features of nodular podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A moderate lymphoplasmacytic infiltrate was joined by mast cells and scattered macrophages; neutrophils and eosinophils were sparse."
    explanation: >-
      The human counterpart, so this node does not rest on rabbit data alone:
      the infiltrate in affected human skin is lymphoplasmacytic with mast cells
      and macrophages, and conspicuously not neutrophilic.
  - reference: PMID:38448477
    reference_title: "Evidence for immune activation in pathogenesis of the HLA class II associated disease, podoconiosis."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    snippet: "Price also observed that silicate particles caused subendothelial edema, endolymphangitis, collagenisation and obliteration of the lymphatic lumen"
    explanation: >-
      Names subendothelial oedema and endolymphangitis in human tissue, which is
      this node's exact claim. Graded OTHER and INDIRECT because the sentence is
      this paper's summary of Price's earlier work rather than its own result.

- name: Lymphatic Vessel Wall Collagenization
  description: >-
    Sustained inflammation lays down collagen in and around the lymphatic vessel
    wall. This is the fibrogenic process; the closed lumen it produces is the
    next node.
  biological_scale: TISSUE
  biological_processes:
  - preferred_term: collagen fibril organization
    modifier: INCREASED
    term:
      id: GO:0030199
      label: collagen fibril organization
  downstream:
  - target: Luminal Obliteration and Loss of Conducting Lymphatics
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:38448477
    reference_title: "Evidence for immune activation in pathogenesis of the HLA class II associated disease, podoconiosis."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: OTHER
    snippet: "Price also observed that silicate particles caused subendothelial edema, endolymphangitis, collagenisation and obliteration of the lymphatic lumen"
    explanation: >-
      Names collagenisation of the lymphatic wall in sequence with the
      obliteration it causes, which is the split this pair of nodes represents.
      Graded OTHER and INDIRECT: the sentence summarises Price's earlier work
      rather than reporting this paper's own result.
  - reference: PMID:25401490
    reference_title: "Histopathological and immunohistochemical features of nodular podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dermal collagen bundles were thickened, and elastic fibers were dramatically reduced."
    explanation: The collagen deposition, measured in affected human skin.

- name: Luminal Obliteration and Loss of Conducting Lymphatics
  description: >-
    The end state of the fibrosis: vessels that no longer carry lymph. Biopsy
    series count fewer lymphatic vessels in affected skin, and a subdermal
    conducting lymphatic in an affected foot was shown to be fibrosed and
    impermeable to injected dye - the functional proof, not just the
    histological one.
  biological_scale: TISSUE
  downstream:
  - target: Lymphatic Obstruction and Lymph Stasis
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:2604475
    reference_title: "Soil particles in the tissues of the foot in endemic elephantiasis of the lower legs."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The conducting lymphatic in the subdermal tissue is found to be impermeable to Patent Blue Violet dye and to be fibrosed."
    explanation: >-
      The functional demonstration that the fibrosed vessel no longer conducts -
      dye impermeability alongside the histological fibrosis.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as thickened collagen bundles."
    explanation: >-
      The advanced-stage histopathology, which reports a reduced number of
      lymphatic vessels alongside the sclerosis.

- name: Lymphatic Obstruction and Lymph Stasis
  description: >-
    Lymph cannot leave the limb. The clinical result is swelling that begins at
    the feet and progressively involves the legs, bilateral in about seven of
    eight patients, frequently asymmetric between them, and in almost all cases
    staying below the knee.
  biological_scale: ORGANISM
  locations:
  - preferred_term: lower limb
    term:
      id: UBERON:0008784
      label: lower limb segment
  downstream:
  - target: Dermal Sclerosis and Nodule Formation
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "mineral particles in red-clay soils are absorbed through the skin of the foot and engulfed by macrophages in the lower limb lymphatic system, inducing an inflammatory response in the lymphatic vessels, which results in fibrosis and obstruction of the vessel lumen."
    explanation: Names lymphatic obstruction as the terminal step of the mechanism.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In 251 (86.9%) patients, both legs were affected by podoconiosis and in 38 (13.1%) only one leg was affected."
    explanation: >-
      The laterality figures behind the "bilateral but not universal" claim,
      from a 289-patient series.

- name: Dermal Sclerosis and Nodule Formation
  description: >-
    Chronic stasis lays down collagen in the dermis, producing thickened
    sclerotic bundles and the firm nodules of established disease. Nodules are
    present in about two fifths of patients and are what nodulectomy removes.
  biological_scale: TISSUE
  locations:
  - preferred_term: skin of the lower leg and foot
    term:
      id: UBERON:0001511
      label: skin of leg
  biological_processes:
  - preferred_term: collagen fibril organization
    modifier: INCREASED
    term:
      id: GO:0030199
      label: collagen fibril organization
  downstream:
  - target: Epidermal Hyperkeratosis and Barrier Failure
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as thickened collagen bundles."
    explanation: >-
      The dermal half of the advanced-stage histopathology - thickening and
      sclerosis with thickened collagen bundles.
  - reference: PMID:25401490
    reference_title: "Histopathological and immunohistochemical features of nodular podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dermal collagen bundles were thickened, and elastic fibers were dramatically reduced."
    explanation: >-
      The second biopsy series' account of the same change, adding the elastic
      fibre loss.

- name: Epidermal Hyperkeratosis and Barrier Failure
  description: >-
    The epidermis thickens into verrucous acanthosis and the warty "mossy"
    plaques the disease is named for, present in about three quarters of
    patients. Curated separately from the dermal change because it is a
    different tissue layer and, more importantly, a different claim: this is
    where the skin stops being a barrier, and it is the node that leads to the
    acute attacks.
  biological_scale: TISSUE
  locations:
  - preferred_term: skin of the lower leg and foot
    term:
      id: UBERON:0001511
      label: skin of leg
  downstream:
  - target: Acute Dermatolymphangioadenitis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Fissured, hyperkeratotic skin is the portal of entry for the skin flora
      that precipitate the acute attacks.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "220 (77.5%) patients had warty lesions, 114 (39.4%) had nodules."
    explanation: The frequencies of warty lesions and nodules in a 289-patient series.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as thickened collagen bundles."
    explanation: >-
      The epidermal half of the same histopathology - epidermal thickening and
      verrucous acanthosis.
  - reference: PMID:33558538
    reference_title: "Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These include dermal nodules and a rough, velvet-like appearance to the skin known as mossy changes which are pathognomonic for the disease."
    explanation: >-
      States that the mossy change is pathognomonic, which is why this node
      carries diagnostic weight rather than only descriptive weight.

- name: Acute Dermatolymphangioadenitis
  description: >-
    Recurrent episodes of fever, pain, erythema and abrupt worsening of the
    swelling, precipitated by bacteria entering through fissured skin. Each
    episode damages the lymphatics further, so the entry models it as feeding
    back into the fibrotic lesion rather than as a terminal complication. It is
    also the outcome every trial in this disease is powered on, because it is
    what patients lose working days to.
  biological_scale: ORGANISM
  downstream:
  - target: Lymphatic Vessel Wall Collagenization
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The self-reinforcing loop. Repeated acute inflammation is held to
      accelerate the underlying fibrosis; the step is described consistently in
      the clinical literature but has not been dissected, so it is curated with
      unknown intermediates.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Increased episodes of ADLA were significantly associated with stage 3-5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis."
    explanation: >-
      Ties attack frequency to advanced stage, which is the observation behind
      the feedback edge - and notes that burning pain instead marks early
      disease.
  - reference: PMID:37612446
    reference_title: "Tropical leg lymphedema caused by podoconiosis is associated with increased colonisation by anaerobic bacteria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lymphedema can lead to skin lesions, which can serve as entry points for bacteria that may cause ADLA attacks leading to progression of the lymphedema."
    explanation: >-
      States the skin-breach-to-attack-to-progression sequence, which is the
      loop this node closes. The source hedges it ("can", "may") and so does
      this entry: the edge is curated INDIRECT_UNKNOWN_INTERMEDIATES.
  - reference: PMID:37612446
    reference_title: "Tropical leg lymphedema caused by podoconiosis is associated with increased colonisation by anaerobic bacteria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We revealed a positive correlation between increasing lymphedema severity and non-commensal anaerobic bacteria, especially Anaerococcus provencensis, as well as a negative correlation with the presence of Corynebacterium, a constituent of normal skin flora."
    explanation: >-
      Identifies what colonises the affected skin and how it tracks severity -
      anaerobes up, normal commensal Corynebacterium down. The correlation is
      with stage, so it does not establish direction on its own.

phenotypes:
- category: Lymphatic
  name: Bilateral Below-Knee Lower-Limb Lymphedema
  description: >-
    Swelling that begins at the feet and works up the legs, bilateral in about
    seven of eight patients and frequently asymmetric between them in stage or
    in type. It stays below the knee in almost all cases - only 1.4% of one
    large series had swelling above it. Unilateral involvement is described as a
    clinical variant rather than the rule.
  phenotype_term:
    preferred_term: bilateral below-knee lymphoedema of the lower limbs
    term:
      id: HP:0001004
      label: Lymphedema
    clinical_course: PROGRESSIVE
  frequency: VERY_FREQUENT
  diagnostic: true
  reports_on:
  - target: Lymphatic Obstruction and Lymph Stasis
    relationship: READOUT_OF
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In 251 (86.9%) patients, both legs were affected by podoconiosis and in 38 (13.1%) only one leg was affected."
    explanation: >-
      The laterality split in a 289-patient series - bilateral in 86.9%, which
      is what the VERY_FREQUENT tag rests on.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Podoconiosis is a localised disease, primarily starting from the feet, progressively involving the legs, yet in most cases remaining below the knee."
    explanation: >-
      The distribution as the source states it - starting at the feet,
      progressing up the legs, mostly staying below the knee. Curated in the
      source's own terms rather than as "ascending", which no cited source says.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A small number (1.4%) of patients had leg swelling extending above the knee."
    explanation: The figure behind the below-knee claim.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "104 (36%) patients had asymmetrical stages of the two legs and 51 (18.5%) also had asymmetry in the type of lymphoedema (one leg waterbag and the other fibrotic/sclerotic)."
    explanation: >-
      The asymmetry figures. Note these are asymmetry of stage (36%) and of type
      (18.5%), not of presence - which is why the description says "frequently"
      rather than treating asymmetry as universal.

- category: Integumentary
  name: Mossy Warty Skin Lesions
  description: >-
    Hyperkeratotic, verrucous, moss-like plaques on the foot and lower leg. The
    change is pathognomonic and gives the disease its common name.
  phenotype_term:
    preferred_term: mossy warty hyperkeratotic plaques of the foot and lower leg
    term:
      id: HP:0000962
      label: Hyperkeratosis
  frequency: FREQUENT
  diagnostic: true
  reports_on:
  - target: Epidermal Hyperkeratosis and Barrier Failure
    relationship: READOUT_OF
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "220 (77.5%) patients had warty lesions, 114 (39.4%) had nodules."
    explanation: >-
      77.5% carried warty lesions. Tagged FREQUENT rather than VERY_FREQUENT
      because the figure sits just below the 80% band boundary.
  - reference: PMID:33558538
    reference_title: "Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These include dermal nodules and a rough, velvet-like appearance to the skin known as mossy changes which are pathognomonic for the disease."
    explanation: States that the mossy appearance is pathognomonic for the disease.

- category: Integumentary
  name: Fibrotic Skin Nodules
  description: >-
    Firm, woody nodules on the dorsum of the foot and lower leg in established
    disease. They resist conservative management and are the target of
    nodulectomy.
  phenotype_term:
    preferred_term: woody fibrotic nodules of the foot and lower leg
    term:
      id: HP:0200036
      label: Skin nodule
  frequency: FREQUENT
  reports_on:
  - target: Dermal Sclerosis and Nodule Formation
    relationship: READOUT_OF
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "220 (77.5%) patients had warty lesions, 114 (39.4%) had nodules."
    explanation: 39.4% had nodules in the same series - the FREQUENT band.

- category: Infectious
  name: Recurrent Acute Dermatolymphangioadenitis
  description: >-
    Acute episodes of fever, limb pain, erythema and worsening swelling from
    bacterial entry through fissured skin. Frequency rises with disease stage.
  phenotype_term:
    preferred_term: recurrent acute dermatolymphangioadenitis
    term:
      id: HP:0100658
      label: Cellulitis
    temporality: RECURRENT
  frequency: VERY_FREQUENT
  reports_on:
  - target: Acute Dermatolymphangioadenitis
    relationship: READOUT_OF
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Increased episodes of ADLA were significantly associated with stage 3-5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis."
    explanation: >-
      Establishes the stage dependence - attacks concentrate in advanced
      disease.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "About 86% of the cases in our study had at least one episode of ADLA during the three-month period preceding the date of examination."
    explanation: >-
      The proportion the VERY_FREQUENT tag rests on, and the reason it is this
      figure rather than any other in the entry: 86% of patients in a
      289-patient series restricted to podoconiosis, over a three-month window.
      That is a patient proportion in a disease-specific cohort, which is what
      the frequency band is defined on.
  - reference: PMID:29773516
    reference_title: "Lymphoedema management to prevent acute dermatolymphangioadenitis in podoconiosis in northern Ethiopia (GoLBeT): a pragmatic randomised controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The ratio of incidence rate in the intervention group to that of the control group was 0·81 (0·74 to 0·89; p<0·0001), with a rate difference of -4·5 (-5·1 to -3·8) episodes per person-year."
    explanation: >-
      The episode rate, which is what makes this the outcome trials are powered
      on. It is a rate per person-year, not a proportion of patients, so it does
      not by itself set a frequency band.
  - reference: PMID:33348721
    reference_title: "Addition of Lymphatic Stimulating Self-Care Practices Reduces Acute Attacks among People Affected by Moderate and Severe Lower-Limb Lymphedema in Ethiopia, a Cluster Randomized Controlled Trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was a significant between-group difference in patients who reported any acute attacks over the study period (control n = 22 (38%), intervention n = 7 (12%), p = 0.014)."
    explanation: >-
      A second patient proportion, curated for the treatment effect it shows
      rather than as the frequency basis. It is deliberately *not* what the band
      rests on: this trial enrolled in Ethiopia and Bangladesh and made no
      attempt to separate podoconiosis from filarial lymphoedema, so its 38%
      describes a mixed-etiology cohort. See the accompanying item for that
      caveat in the authors' own words.
  - reference: PMID:33348721
    reference_title: "Addition of Lymphatic Stimulating Self-Care Practices Reduces Acute Attacks among People Affected by Moderate and Severe Lower-Limb Lymphedema in Ethiopia, a Cluster Randomized Controlled Trial."
    supports: NO_EVIDENCE
    evidence_source: HUMAN_CLINICAL
    snippet: "we made no attempt to differentiate the cause of lymphedema in our study."
    explanation: >-
      Graded NO_EVIDENCE against this phenotype's frequency: the authors state
      they did not differentiate the cause of lymphoedema, so the trial's
      proportions cannot be read as podoconiosis-specific. Recorded because an
      earlier draft of this entry used its 38% to set the frequency band, and
      the reason that was wrong is worth keeping visible.

- category: Musculoskeletal
  name: Ankle Ankylosis
  description: >-
    Fixation of the ankle joint in stage 5 disease, and the main driver of
    mobility loss once it appears.
  phenotype_term:
    preferred_term: ankylosis of the ankle joint
    term:
      id: HP:0031013
      label: Ankylosis
  reports_on:
  - target: Lymphatic Obstruction and Lymph Stasis
    relationship: READOUT_OF
  notes: >-
    Curated without a frequency: the cited series bands its patients as stage
    1-2 versus stage 3-5 and does not report how many reach stage 5. It is
    attached to the lymph-stasis node rather than to the skin node because the
    fibrosis that fixes the joint is periarticular, and this entry has no
    periarticular node - the reader should not infer that skin change causes
    the ankylosis.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "H) Stage 5: fibrotic globular swelling of the left foot and ankle with ankylosis of the ankle joint, multiple areas of scarring (from traditional bloodletting)."
    explanation: >-
      Places ankylosis of the ankle joint in stage 5, quoted from the series'
      figure legend.

stages:
- name: Stage 1
  description: >-
    Early and reversible. Burning pain in the feet, splaying of the forefoot,
    accentuated skin markings over the metatarsophalangeal joints.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "B) Stage 1: splaying of the right forefoot, accentuation of the skin markings on the metatarsophalangeal joint."
    explanation: The clinical description of this stage, from the series' own figure legend.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Increased episodes of ADLA were significantly associated with stage 3-5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis."
    explanation: >-
      Places burning pain in the early stages, which is the symptom this stage
      is recognised by.
- name: Stage 2
  description: >-
    Bilateral lymphoedema below the knee, still soft, with warty hyperkeratotic
    papules beginning to cover the dorsum of the feet.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "C) Stage 2: bilateral lymphoedema below the knee."
    explanation: The stage description from the series' figure legend.
- name: Stage 3
  description: >-
    Fibrotic, non-pitting oedema below the knee, with early nodules and skin
    changes. The transition from stage 2 to stage 3 is where reversibility is
    lost.
  notes: >-
    Curated without its own evidence item. The cached source illustrates stages
    1, 2, 4 and 5 in its figure legends but not stage 3 separately; the
    description follows the five-stage system the source cites rather than a
    quotable sentence, and is flagged here rather than given a snippet that does
    not say it.
- name: Stage 4
  description: >-
    Non-pitting oedematous swelling extending above the knee, with skin
    depigmentation around the ankle. Reached by only a small minority.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "G) Stage 4 (right) and stage 2 (left). Right foot: non pitting oedematous swelling of the leg extending above the knee with an area of skin depigmentation around the ankle."
    explanation: >-
      The stage description, and incidentally a demonstration that the two legs
      can sit at different stages in one patient.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A small number (1.4%) of patients had leg swelling extending above the knee."
    explanation: >-
      How rarely this stage is reached - 1.4% of the series had swelling above
      the knee at all.
- name: Stage 5
  description: >-
    Fixed, globular, woody swelling with ankylosis of the ankle joint, multiple
    nodules and band-like redundant skin folds.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "H) Stage 5: fibrotic globular swelling of the left foot and ankle with ankylosis of the ankle joint, multiple areas of scarring (from traditional bloodletting)."
    explanation: >-
      The stage description, which is also the source of the ankylosis
      phenotype's evidence.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We recruited 289 patients for the study, 178 (61.6%) had stage 1 or 2 podoconiosis, and 111(38.4%) stage 3 to 5 podoconiosis."
    explanation: >-
      The distribution across the two stage bands in a community series - about
      three fifths early, two fifths advanced.

histopathology:
- name: Verrucous Acanthosis with Thickened Collagen Bundles and Reduced Lymphatic Vessels
  description: >-
    The advanced-stage biopsy picture: epidermal and dermal thickening,
    verrucous acanthosis, a predominantly lymphoplasmacytic infiltrate, dilated
    and ectatic but fewer lymphatic vessels, eccrine ductal hyperplasia, and
    sclerotic collagen.
  finding_term:
    preferred_term: verrucous acanthosis with dermal sclerosis and reduced lymphatic vessels
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as thickened collagen bundles."
    explanation: The full histopathological description this finding records.

- name: Mast Cell and Macrophage Infiltrate with Elastic Fibre Loss
  description: >-
    A second biopsy series adds the cellular detail: a moderate lymphoplasmacytic
    infiltrate joined by mast cells and scattered macrophages, with neutrophils
    and eosinophils sparse, dramatically reduced elastic fibres, and lymphatics
    that are reduced in number and mostly not dilated. The cell mix is that of a
    chronic sterile inflammatory process, not an acute infective one.
  finding_term:
    preferred_term: lymphoplasmacytic infiltrate with mast cells and elastic fibre loss
  evidence:
  - reference: PMID:25401490
    reference_title: "Histopathological and immunohistochemical features of nodular podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All specimens showed verrucous acanthosis and papillomatosis. Eccrine ducts demonstrated hyperplasia, syringofibroadenomatous changes and miliaria. Dermal collagen bundles were thickened, and elastic fibers were dramatically reduced. A moderate lymphoplasmacytic infiltrate was joined by mast cells and scattered macrophages; neutrophils and eosinophils were sparse. Blood vessels were increased, dilated, and often sclerotic while lymphatics were reduced and largely not dilated."
    explanation: >-
      The cellular and structural findings this record names, including the
      sparse neutrophils that argue against an infective picture in the steady
      state.
  - reference: PMID:25401490
    reference_title: "Histopathological and immunohistochemical features of nodular podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Podoconiosis demonstrates distinctive changes of chronic lymphedema with extensive sclerosis, loss of elastic fibers, verrucous acanthosis (not HPV induced) and reactive changes of eccrine structures."
    explanation: >-
      The authors' summary, which also flags mast cells and macrophages as
      candidate participants rather than bystanders.

- name: Verrucous Acanthosis Without Human Papillomavirus
  description: >-
    The warty, papillomatous surface change is not virally driven. Every
    specimen tested was HPV-PCR negative, which removes the obvious alternative
    explanation for a verrucous epidermis and keeps the change attributable to
    chronic lymphoedema.
  finding_term:
    preferred_term: verrucous acanthosis, HPV-negative
  evidence:
  - reference: PMID:25401490
    reference_title: "Histopathological and immunohistochemical features of nodular podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HPV-PCR was negative in all specimens."
    explanation: >-
      Supports this record, which asserts the verrucous change is *not* virally
      driven; a negative PCR across all specimens is exactly that claim's
      evidence. Graded SUPPORT rather than REFUTE because `supports` is relative
      to the record it sits on, not to the hypothesis the result rules out.

environmental:
- name: Long-term barefoot contact with red-clay soil derived from alkalic volcanic rock
  description: >-
    The necessary environmental cause. Exposure is transdermal rather than
    inhalational, occurs over years of subsistence farming without footwear, and
    is determined by soil geochemistry - endemic areas sit on alkalic volcanic
    bedrock at high altitude with high rainfall, the conditions that weather it
    into the implicated clays.
  exposure_term:
    preferred_term: barefoot contact with alkalic volcanic red-clay soil
    term:
      id: ECTO:7000012
      label: exposure to soil
  exposure_classifications:
    hazard_agent_type:
    - classification_value: CHEMICAL
      notes: >-
        Classified chemical on the same basis as the mineral-dust exposures in
        silicosis and coal workers' pneumoconiosis - the operative agent is a
        silicate particle, not a living organism. The secondary bacterial
        infection that drives acute attacks is a consequence of the skin
        breakdown, not the exposure being classified here.
    exposure_route:
    - classification_value: DERMAL
      notes: >-
        The distinguishing feature against the other mineral-dust entries in
        this knowledge base that carry `exposure_classifications` - silicosis,
        coal workers' pneumoconiosis and asbestosis all record INHALATION. Note
        that dermal routes are not unique to podoconiosis across the KB as a
        whole: `Chronic_Beryllium_Disease` curates a "Dermal beryllium exposure"
        entry as a second route to sensitization, though that file carries no
        `exposure_classifications` block to compare against.
    exposure_duration:
    - classification_value: CHRONIC
    exposome_domain:
    - classification_value: SPECIFIC_EXTERNAL
  notes: >-
    No IARC group is recorded. IARC has not classified this soil exposure, and
    podoconiosis is not a neoplastic outcome. No GHS class is recorded either:
    the exposure is a natural soil rather than a classified substance.
  influences_mechanisms:
  - target: Transdermal Entry of Silicate Mineral Particles
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Barefoot soil contact is the route by which the mineral particles reach
      the skin at all; there is no other described exposure pathway.
    evidence:
    - reference: PMID:40898820
      reference_title: "Podoconiosis: a comprehensive clinical review and strategies for control and elimination."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "It arises due to prolonged exposure of bare feet to irritant red-clay soils in genetically susceptible individuals."
      explanation: >-
        States the exposure and the susceptibility requirement together, which
        is exactly what this edge and its downstream HLA node jointly assert.
        Graded OTHER: the source is a narrative review and the sentence is its
        own summary statement, not a reported result.
  evidence:
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Podoconiosis is a tropical lymphedema resulting from long-term barefoot exposure to red-clay soil derived from volcanic rock. The World Health Organization recently designated it as a neglected tropical disease. Podoconiosis develops in only a subgroup of exposed people, and studies have shown familial clustering with high heritability (63%)."
    explanation: The canonical statement of the exposure and its duration.
  - reference: PMID:40623043
    reference_title: "Associations between podoconiosis and pedogenic factors globally - A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nine studies found a correlation between podoconiosis occurrence and regions with underlying alkalic volcanic bedrock, and six linked pedogenic factors (altitude and rainfall) with disease occurrence. Several studies linked specific soil mineralogy and geochemistry with endemic regions, including an abundance of phyllosilicate clay minerals, quartz, and trace elements, notably iron, beryllium and zirconium."
    explanation: >-
      The bedrock, pedogenic and mineralogical correlates that make this a
      geochemically defined exposure rather than a geographic one.
  - reference: PMID:40623043
    reference_title: "Associations between podoconiosis and pedogenic factors globally - A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, it remains unclear whether these are covariates or direct contributors to the pathogenesis of the disease"
    explanation: >-
      The systematic review's own caution that the mineral correlations may be
      covariates rather than causes. Curated because this entry names specific
      minerals and should not imply more than the source does.

genetic:
- name: HLA class II susceptibility haplotype
  gene_term:
    preferred_term: HLA-DQA1
    term:
      id: hgnc:4942
      label: HLA-DQA1
  relationship_type: SUSCEPTIBILITY
  variant_origin: GERMLINE
  frequency: common susceptibility variants, lead SNP odds ratio approximately 1.5-2.4
  notes: >-
    Curated as a susceptibility locus, not a causative gene. `gene_term` carries
    HLA-DQA1 because the slot is single-valued and the first genome-wide
    significant SNP sits 5.8 kb from it; the replication study's lead SNP lies
    near HLA-DRB1, and DQB1 is implicated by the risk haplotype. All three are
    bound on the pathophysiology node. Heritability is estimated at 63% and the
    sibling recurrence risk ratio at 5.07, so the genetic contribution is
    substantial - but no variant is sufficient without the soil exposure, and no
    locus outside HLA class II reached significance in a better-powered second
    genome-wide study.
  evidence:
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found a genomewide significant association of podoconiosis with the single-nucleotide polymorphism (SNP) rs17612858, located 5.8 kb from the HLA-DQA1 locus (in the allelic model: odds ratio, 2.44; 95% confidence interval [CI], 1.82 to 3.26; P=1.42×10(-9); and in the additive model: odds ratio, 2.19; 95% CI, 1.66 to 2.90; P=3.44×10(-8))"
    explanation: The primary genome-wide association result.
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HLA typing showed the alleles HLA-DRB1*0701 (odds ratio, 2.00), DQA1*0201 (odds ratio, 1.91), and DQB1*0202 (odds ratio, 1.79) and the HLA-DRB1*0701-DQB1*0202 haplotype (odds ratio, 1.92) were risk variants for podoconiosis."
    explanation: The HLA-typed risk alleles and haplotype behind the SNP signal.
  - reference: PMID:33558538
    reference_title: "Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fourteen SNPs in the HLA class II region showed significant genome-wide association (P < 5.0 × 10-8) with podoconiosis. The lead SNP was rs9270911 (P = 5.51 × 10-10; OR 1.53; 95% CI 1.34-1.74), located near HLA-DRB1."
    explanation: >-
      Replication across three Ethiopian populations, with the lead signal
      shifting to HLA-DRB1.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "188 (64.1%) had a family history of podoconiosis."
    explanation: >-
      Graded INDIRECT: family history in two thirds of patients is consistent
      with a heritable component but does not by itself separate shared genes
      from shared soil, since families farm the same land.

diagnosis:
- name: Clinical Diagnosis with Exclusion of Lymphatic Filariasis
  description: >-
    There is no confirmatory test. Diagnosis rests on the exposure history, the
    bilateral below-knee distribution and the mossy skin change, with a negative
    filarial antigen test to exclude the principal mimic. The HLA association is
    a research finding and is not a diagnostic test.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dermatologists performed a patient history, physical examination, filariasis test strip, and skin biopsy for histopathologic examination."
    explanation: >-
      The assessment sequence used in a large field series, including the
      filariasis test strip that does the excluding.
  - reference: PMID:33558538
    reference_title: "Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These include dermal nodules and a rough, velvet-like appearance to the skin known as mossy changes which are pathognomonic for the disease."
    explanation: >-
      The pathognomonic sign that carries the positive half of the diagnosis
      once filariasis is excluded.

differential_diagnoses:
- name: Lymphatic Filariasis
  description: >-
    The principal differential and the reason a filarial antigen test is part of
    every case definition. The distinction this entry curates is mechanistic
    rather than a bedside rule of thumb: in filariasis the lymphatic disruption
    is proximal, at worm nests in the groin or armpits, whereas in podoconiosis
    the insult enters at the feet and the disease stays localised to the legs.
    The two are co-endemic in a number of countries, so geography does not
    settle it either.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Dermatologists performed a patient history, physical examination, filariasis test strip, and skin biopsy for histopathologic examination."
    explanation: >-
      Shows the exclusion being performed in practice - the test strip is part
      of the standard workup, not an optional extra.
  - reference: PMID:33348721
    reference_title: "Addition of Lymphatic Stimulating Self-Care Practices Reduces Acute Attacks among People Affected by Moderate and Severe Lower-Limb Lymphedema in Ethiopia, a Cluster Randomized Controlled Trial."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Whereas the lymphatic disruption in LF is proximal (worm nests in the groin or armpits), in podoconiosis the exposure is at the feet"
    explanation: >-
      The mechanistic contrast this record now rests on - proximal worm nests
      versus distal soil entry. Graded OTHER: the sentence is the paper's
      framing of the two diseases rather than a result of its trial.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Podoconiosis is a localised disease, primarily starting from the feet, progressively involving the legs, yet in most cases remaining below the knee."
    explanation: >-
      The localisation half of the contrast, in the source's own words. An
      earlier draft of this record asserted an "ascending" versus "descending"
      distinction and groin sparing; no cited source says any of that, and it
      has been replaced with what the sources do say.
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Podoconiosis is a tropical lymphedema resulting from long-term barefoot exposure to red-clay soil derived from volcanic rock. The World Health Organization recently designated it as a neglected tropical disease. Podoconiosis develops in only a subgroup of exposed people, and studies have shown familial clustering with high heritability (63%)."
    explanation: >-
      Graded INDIRECT: the sentence establishes podoconiosis as a
      soil-exposure disease rather than an infection, which is the basis for
      the distinction, without itself comparing the two conditions.

treatments:
- name: Lymphoedema Self-Care Package
  description: >-
    Foot hygiene, skin care, bandaging, exercise, elevation, and consistent use
    of socks and shoes, delivered through lay community agents. This is the
    mainstay and the only management with randomised evidence in this disease.
    Its measured effect is on acute attacks rather than on limb size, and the
    effect is real but partial - about a fifth fewer episodes, against a
    baseline of more than twenty per person-year.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Rehabilitation
    term:
      id: NCIT:C15315
      label: Rehabilitation
  target_mechanisms:
  - target: Acute Dermatolymphangioadenitis
    description: >-
      Hygiene and emollients close the portals of bacterial entry created by
      fissured hyperkeratotic skin, which is the step the trial's primary
      outcome measures.
  evidence:
  - reference: PMID:29773516
    reference_title: "Lymphoedema management to prevent acute dermatolymphangioadenitis in podoconiosis in northern Ethiopia (GoLBeT): a pragmatic randomised controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients were randomly assigned (1:1) to either receive a package containing instructions for foot hygiene, skin care, bandaging, exercises, and use of socks and shoes, with support by lay Community Podoconiosis Agents at monthly meetings (intervention group)"
    explanation: The contents of the package, which is what this treatment describes.
  - reference: PMID:29773516
    reference_title: "Lymphoedema management to prevent acute dermatolymphangioadenitis in podoconiosis in northern Ethiopia (GoLBeT): a pragmatic randomised controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The ratio of incidence rate in the intervention group to that of the control group was 0·81 (0·74 to 0·89; p<0·0001), with a rate difference of -4·5 (-5·1 to -3·8) episodes per person-year."
    explanation: >-
      The effect estimate. Quoted with the absolute rates attached because the
      rate ratio alone hides how high the baseline burden is.
  - reference: PMID:29773516
    reference_title: "Lymphoedema management to prevent acute dermatolymphangioadenitis in podoconiosis in northern Ethiopia (GoLBeT): a pragmatic randomised controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A simple, inexpensive package of lymphoedema self-care is effective in reducing the frequency and duration of acute dermatolymphangioadenitis."
    explanation: The trial's own conclusion and recommendation.
  - reference: PMID:33348721
    reference_title: "Addition of Lymphatic Stimulating Self-Care Practices Reduces Acute Attacks among People Affected by Moderate and Severe Lower-Limb Lymphedema in Ethiopia, a Cluster Randomized Controlled Trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was a significant between-group difference in patients who reported any acute attacks over the study period (control n = 22 (38%), intervention n = 7 (12%), p = 0.014)."
    explanation: >-
      A second randomised trial, testing whether adding lymphatic stimulation to
      the standard package helps. It did, on acute attacks.

- name: Nodulectomy
  description: >-
    Surgical excision of woody fibrotic nodules under local anaesthesia, wounds
    left to heal by secondary intention under compression. Reserved for nodules
    that do not respond to conservative care. It improves quality of life and,
    unexpectedly for a debulking procedure, reduces acute attack frequency.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Surgical Procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_mechanisms:
  - target: Dermal Sclerosis and Nodule Formation
    description: >-
      The procedure removes the fibrotic nodules this node produces; it does not
      address the lymphatic obstruction upstream of them.
  evidence:
  - reference: PMID:33481805
    reference_title: "Surgical debulking of podoconiosis nodules and its impact on quality of life in Ethiopia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The DLQI values were significantly better six months after surgery than before surgery (P<0.0001)."
    explanation: The quality-of-life outcome at six months.
  - reference: PMID:33481805
    reference_title: "Surgical debulking of podoconiosis nodules and its impact on quality of life in Ethiopia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Also the number of ADLA episodes per three months was significantly lower six months after surgery than before surgery (P<0.0001)."
    explanation: >-
      The acute-attack reduction, which is the more surprising result: removing
      nodules also removed some of the infection risk.
  - reference: PMID:33481805
    reference_title: "Surgical debulking of podoconiosis nodules and its impact on quality of life in Ethiopia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Excisions after nodulectomy were left to heal by secondary intention with compression bandaging."
    explanation: >-
      The wound-management detail that makes this a resource-appropriate
      procedure rather than one requiring a theatre and grafting.

- name: Antibiotic Therapy for Acute Attacks
  description: >-
    Antibiotics, penicillin among them, are the recommended treatment for
    interrupting an acute dermatolymphangioadenitis episode. Curated with the
    qualifier the source attaches to it and that this entry will not drop: in
    the remote rural populations where the disease actually occurs, they are not
    routinely available. The recommendation and its reach are different claims.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_mechanisms:
  - target: Acute Dermatolymphangioadenitis
    description: >-
      Antibiotics act on the bacterial arm of the acute episode, not on the
      lymphatic obstruction that produced the portal of entry.
  evidence:
  - reference: PMID:29773516
    reference_title: "Lymphoedema management to prevent acute dermatolymphangioadenitis in podoconiosis in northern Ethiopia (GoLBeT): a pragmatic randomised controlled trial."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Antibiotic therapy (including penicillin), which has been recommended for interruption of acute dermatolymphangioadenitis episodes,17 is not routinely available for patients in remote rural populations in Ethiopia."
    explanation: >-
      Carries both halves of the claim in one sentence - the recommendation and
      the availability caveat. Graded OTHER: the sentence is this trial's
      background framing, citing an earlier recommendation, not a result of the
      trial itself. No trial of antibiotic therapy in podoconiosis is cited in
      this entry.
  notes: >-
    No specific agent is bound. The source names penicillin as an example inside
    a general recommendation, and no cited source in this entry reports a
    regimen, so `therapeutic_agent` is left absent rather than fixed on one drug.

- name: Consistent Footwear Use
  description: >-
    Shoes are the primary prevention, and in early-stage disease they are also
    treatment. Because the exposure is transdermal and the early lymphoedema is
    reversible, interrupting soil contact can halt or reverse stage 1-2 disease.
    This is the intervention that makes podoconiosis eliminable in a way its
    fellow lymphoedemas are not.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: consistent footwear use to interrupt soil contact
    term:
      id: NCIT:C15843
      label: Preventive Intervention
  target_mechanisms:
  - target: Chronic Barefoot Contact with Alkalic Volcanic Clay Soil
    description: >-
      Footwear acts on the exposure itself rather than on any downstream
      mechanism, which is why it can prevent as well as treat.
  evidence:
  - reference: PMID:40898820
    reference_title: "Podoconiosis: a comprehensive clinical review and strategies for control and elimination."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Early intervention, including consistent use of footwear and improved foot hygiene, can greatly reduce disease burden."
    explanation: >-
      States the effect of footwear and hygiene on disease burden. Graded OTHER
      because it is a review's summary statement rather than a measured result.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In stages 1 and 2, simple lymphoedema management can completely reverse the clinical changes, but if the condition is not managed with appropriate foot care and consistent shoe wearing, it can lead to subsequent ir"
    explanation: >-
      The reversibility claim this treatment rests on, stated for stages 1 and 2
      and tied to consistent shoe wearing. Without it the description's "halt or
      reverse" would be asserting more than the footwear evidence shows.
  - reference: PMID:37719165
    reference_title: "Epidemiology of podoconiosis in sub-Saharan Africa: A systematic review and meta-analysis."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Walking barefoot adjusted odd ratio (AOR) 5.35 (95% CI: 1.65, 9.05), p = 0.001, not washing feet with soap and water regularly AOR 2.8 (95% CI: 1.16, 4.44, p = 0.001), and an increased age AOR 2.23 (95% CI: 1.25, 5.58) were factors significantly associated with the prevalence of podoconiosis."
    explanation: >-
      Graded INDIRECT: the odds ratio is for walking barefoot as a risk factor,
      so the protective effect of footwear follows by inversion rather than
      being measured directly. No randomised trial of footwear exists.

clinical_trials:
- name: ISRCTN67805210
  phase: NOT_APPLICABLE
  status: COMPLETED
  description: >-
    GoLBeT, the Gojjam Lymphoedema Best Practice Trial: a pragmatic
    single-blind randomised controlled trial of a community-delivered
    lymphoedema self-care package in northern Ethiopia, powered on acute
    dermatolymphangioadenitis episodes. Results published as PMID:29773516.
  target_phenotypes:
  - preferred_term: recurrent acute dermatolymphangioadenitis
    term:
      id: HP:0100658
      label: Cellulitis
  evidence:
  - reference: ICTRP:ISRCTN67805210
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "| Study design | Pragmatic single-blind randomized controlled trial (Treatment) |"
    explanation: >-
      The registry record establishing the trial's design. Graded OTHER because
      a registration document is not itself study evidence; the results are
      curated on the Lymphoedema Self-Care Package treatment.
  notes: >-
    Keyed on the WHO ICTRP identifier rather than an NCT number - this trial is
    registered with ISRCTN and has no ClinicalTrials.gov record.

- name: ISRCTN16764792
  phase: NOT_APPLICABLE
  status: COMPLETED
  description: >-
    Enhanced self-care for advanced lymphoedema: a comparative study in Ethiopia
    and Bangladesh testing whether adding lymphatic stimulation - self-massage
    and deep breathing - to the standard hygiene package improves outcomes.
    Results published as PMID:33348721.
  evidence:
  - reference: ICTRP:ISRCTN16764792
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "| Countries of recruitment | Bangladesh; Ethiopia |"
    explanation: >-
      The registry record. Listed because the trial's published results are
      curated on the self-care treatment and the identifier should be
      machine-findable rather than sitting in prose.

inheritance:
- name: Non-Mendelian inheritance
  inheritance_term:
    preferred_term: complex HLA class II-associated susceptibility
    term:
      id: HP:0001426
      label: Non-Mendelian inheritance
  description: >-
    Podoconiosis is inherited as a susceptibility, not as a disease. A
    segregation analysis of multi-generational Ethiopian families fitted an
    autosomal co-dominant major-gene model with a sibling recurrence risk ratio
    of 5.07 and heritability of 0.63; two subsequent genome-wide association
    studies located the signal in the HLA class II region and found nothing
    outside it. The entry binds `HP:0001426` rather than `HP:0032113`
    (Semidominant inheritance) because the latter sits under *Mendelian
    inheritance* in HPO, and no genotype produces podoconiosis without the soil
    exposure.
  evidence:
  - reference: PMID:33558538
    reference_title: "Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A segregation analysis of 59 multi-generational podoconiosis families from the Wolaita ethnic group in southwest Ethiopia indicated an autosomal co-dominant pattern of inheritance with an estimated sibling recurrence risk ratio (λs) and heritability of 5.07 and 0.63 respectively"
    explanation: >-
      The segregation model, the sibling recurrence risk ratio and the
      heritability estimate, all in one sentence.
  - reference: PMID:22455414
    reference_title: "HLA class II locus and susceptibility to podoconiosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Podoconiosis is a tropical lymphedema resulting from long-term barefoot exposure to red-clay soil derived from volcanic rock. The World Health Organization recently designated it as a neglected tropical disease. Podoconiosis develops in only a subgroup of exposed people, and studies have shown familial clustering with high heritability (63%)."
    explanation: >-
      Confirms the 63% heritability independently, and states in the same breath
      that the disease develops only in exposed people.

prevalence:
- population: Sub-Saharan Africa
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 2660.0
  rate_low: 2240.0
  rate_high: 3100.0
  rate_denominator: POPULATION
  notes: >-
    Pooled across 16 studies and 2,195,722 individuals. Heterogeneity is
    extreme (I-squared 99.9%), which is expected for a disease whose
    distribution is set by local bedrock - the pooled figure describes the
    region, not any district in it.
  evidence:
  - reference: PMID:37719165
    reference_title: "Epidemiology of podoconiosis in sub-Saharan Africa: A systematic review and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The pooled prevalence of podoconiosis was 2.66 (95% confidence interval (CI): 2.24, 3.10) with heterogeneity index (I2) of 99.9%."
    explanation: The pooled estimate and its confidence interval and heterogeneity index.

- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: RARE
  notes: >-
    About four million people affected globally, concentrated in tropical
    highland regions. Recorded as a case count rather than a rate because the
    source gives an absolute burden without a denominator.
  evidence:
  - reference: PMID:33558538
    reference_title: "Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is estimated that there are 4 million people living with podoconiosis globally, mainly living in highland regions of tropical countries in Africa, South and Central America and southeast Asia"
    explanation: The global burden estimate and its geographic distribution.

epidemiology:
- name: Exposure-Dependent Distribution Set by Bedrock and Climate
  description: >-
    The disease occurs where alkalic volcanic bedrock weathers under high
    altitude and high rainfall into the implicated clays, and where people farm
    that soil barefoot. Both conditions are required, which is why podoconiosis
    is absent from equally volcanic areas where footwear is universal.
  evidence:
  - reference: PMID:40623043
    reference_title: "Associations between podoconiosis and pedogenic factors globally - A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nine studies found a correlation between podoconiosis occurrence and regions with underlying alkalic volcanic bedrock, and six linked pedogenic factors (altitude and rainfall) with disease occurrence. Several studies linked specific soil mineralogy and geochemistry with endemic regions, including an abundance of phyllosilicate clay minerals, quartz, and trace elements, notably iron, beryllium and zirconium."
    explanation: The bedrock and pedogenic correlations behind the distribution.
  - reference: PMID:37719165
    reference_title: "Epidemiology of podoconiosis in sub-Saharan Africa: A systematic review and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Walking barefoot adjusted odd ratio (AOR) 5.35 (95% CI: 1.65, 9.05), p = 0.001, not washing feet with soap and water regularly AOR 2.8 (95% CI: 1.16, 4.44, p = 0.001), and an increased age AOR 2.23 (95% CI: 1.25, 5.58) were factors significantly associated with the prevalence of podoconiosis."
    explanation: >-
      The behavioural half of the requirement, with foot hygiene and age
      alongside it.

progression:
- phase: Reversible Early Disease
  notes: >-
    Stages 1-2. Swelling is soft and pitting and still responds to elevation,
    footwear and hygiene. About three fifths of patients in a community series
    were in this band, which is where the prevention argument has its purchase.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We recruited 289 patients for the study, 178 (61.6%) had stage 1 or 2 podoconiosis, and 111(38.4%) stage 3 to 5 podoconiosis."
    explanation: The stage distribution this phase describes.

- phase: Fixed Fibrotic Disease
  notes: >-
    Stages 3-5. Non-pitting oedema, established dermal sclerosis, nodules and
    eventually ankylosis. Acute attacks become more frequent as the stage
    advances, so the fibrotic phase is also the phase with the highest acute
    burden. Self-care still helps here; reversal does not.
  evidence:
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Increased episodes of ADLA were significantly associated with stage 3-5 podoconiosis (P = 0.002), while burning pain in the feet was more common in stage 1 or 2 podoconiosis."
    explanation: >-
      The association between advanced stage and acute-attack frequency that
      makes this phase clinically distinct.
  - reference: PMID:35604949
    reference_title: "Podoconiosis: Clinical spectrum and microscopic presentations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Stage 3-5 disease was histopathologically characterised by epidermal and dermal thickening, verrucous acanthosis, inflammatory cell infiltrates (predominantly lymphoplasmacytic), dilated and ectatic and a reduced number of lymphatic vessels, eccrine ductal hyperplasia, and sclerosis such as thickened collagen bundles."
    explanation: The histological correlates of the fixed phase.

animal_models:
- name: Intralymphatic silica injection model
  species: Rabbit
  genotype: Wild type
  description: >-
    Fine silica particles injected directly into lymphatic vessels, designed to
    test whether the mineral alone can produce the obstructive lesion and to
    locate its main site of action. It bypasses the skin and the adaptive immune
    system entirely, which is both its power and its limit. The species is taken
    from the record's MeSH indexing (Rabbits); the abstract itself says only
    "animal experiments".
  publication: PMID:3006293
  modeled_mechanisms:
  - target: Endolymphangitis
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: >-
      Silica provoked immediate intense macrophage reaction and later fibrosis
      within lymph vessels, with lymphographic obstruction attributable more to
      the vessels than to the nodes.
    limitations: >-
      Direct intralymphatic injection is not the human exposure route: it skips
      transdermal entry, delivers a bolus rather than a decades-long trickle,
      and uses silica rather than the kaolinite that predominates in human
      lymph node microanalysis. It also cannot model the HLA class II
      susceptibility, since the animals are not selected for it - so the model
      shows the mineral is sufficient for the vessel lesion in an unselected
      host, which is a different claim from the human one.
    divergences:
    - divergence_type: BOUNDARY_OMISSION
      materiality: QUALIFYING
      description: >-
        The plantar skin barrier and the whole transdermal entry step are
        outside the model. Everything this entry curates upstream of the
        lymphatic is untested by it.
    - divergence_type: PROXY_QUANTITY
      materiality: QUALIFYING
      description: >-
        The injected material is fine silica; the quantity the human node
        concerns is chronic kaolinite-dominant silicate deposition arriving via
        macrophage transport. Same mineral class, different species and
        different delivery.
    - divergence_type: POPULATION_MISMATCH
      materiality: INVALIDATING
      description: >-
        Human disease occurs in the subset of exposed people carrying HLA class
        II risk haplotypes. The experimental animals are unselected, so the
        model cannot speak to the susceptibility step that decides who gets the
        disease.
    evidence:
    - reference: PMID:3006293
      reference_title: "The effects of silica on lymph nodes and vessels--a possible mechanism in the pathogenesis of non-filarial endemic elephantiasis."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Intralymphatic silica provoked an immediate and intense macrophage reaction with later fibrosis both within lymph vessels and to a lesser extent within lymph nodes. Lymphography indicated that the consequent obstruction resulted more from the effects of silica on vessels than on nodes."
      explanation: >-
        The experimental result, including the vessel-over-node localisation
        that this entry's chain follows.

discussions:
- discussion_id: podo_soil_trigger_unidentified
  kind: KNOWLEDGE_GAP
  prompt: >-
    Which constituent of alkalic volcanic red clay is the trigger, and how does
    a mineral particle come to be presented by an HLA class II molecule?
  rationale: >-
    This is the hole at the centre of the disease. The exposure is known, the
    susceptibility locus is known and replicated, and the lesion is described in
    detail - but the antigen is not identified, and no mechanism connects a
    silicate particle to class II presentation. Kaolinite, smectite, quartz,
    iron oxides, beryllium and zirconium are all correlated with endemicity and
    none is established as causal; the systematic review that assembled them says
    outright that they may be covariates. Without the trigger there is no
    biomarker, no early diagnostic, and no target - which is why the entry's
    edge from particle transport to the HLA node is curated with unknown
    intermediates rather than as antigen presentation.
  attaches_to:
  - pathophysiology#Lymphatic Transport of Particle-Laden Macrophages
  - pathophysiology#HLA Class II-Restricted CD4 T-Cell Response
  - environmental#Long-term barefoot contact with red-clay soil derived from alkalic volcanic rock

- discussion_id: podo_inverted_mineral_response
  kind: INTERPRETATION
  prompt: >-
    Why do healthy exposed controls mount a larger IL-1beta response to kaolinite
    and chlorite than patients do?
  rationale: >-
    The intuitive model - patients are hypersensitive to the mineral - is
    contradicted by the only in vitro stimulation study in this disease.
    Patients had higher unstimulated TNF-alpha and IL-1beta, but on stimulation
    the controls produced two to three times more IL-1beta. The authors read
    this as persistent in vivo activation, with exhaustion or regulation
    blunting the response to a further hit. The entry curates the result as a
    SUPPORT item on the immune-activation node - it supports that node's
    chronic-activation reading, and `supports` is relative to the record an item
    sits on rather than to the hypothesis the result rules out. It is curated
    rather than omitted because an entry that quietly dropped it would imply a
    hypersensitivity model the evidence does not support. It is a single small
    study and should not be treated as settled either way.
  attaches_to:
  - pathophysiology#Chronic Systemic Immune Activation

- discussion_id: podo_no_animal_model
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Can any existing model system reproduce podoconiosis, given that the disease
    requires both a human HLA class II haplotype and barefoot bipedal soil
    contact?
  rationale: >-
    The only experimental model in the literature injects silica directly into
    lymphatics, which reproduces the vessel lesion while bypassing the skin, the
    exposure route, the mineral species and the susceptibility genotype. There is
    no animal that walks barefoot on volcanic clay carrying a human class II
    risk haplotype, and no natural veterinary counterpart has been described. So
    every mechanistic claim upstream of the lymphatic vessel in this entry rests
    on human tissue and human genetics alone, and the one model available cannot
    arbitrate between the HLA-dependent and HLA-independent routes to the same
    lesion.
  attaches_to:
  - pathophysiology#HLA Class II-Restricted CD4 T-Cell Response
  - animal_models#Rabbit

notes: >-
  Why this entry exists. Podoconiosis is the cleanest gene-environment disease
  available: a mineral exposure with no pathogen and no vector, an HLA class II
  susceptibility replicated across three populations, and a heritability of 63%
  layered on an obligate environmental cause. Neither half produces disease
  alone - mineral particles are found in the lymph nodes of unaffected residents,
  and no genotype causes podoconiosis without the soil.

  Two things are curated as evidence rather than smoothed away. The in vitro
  mineral stimulation result runs against the obvious model and is kept with an
  explanation that says so and a discussion that argues it out. And the
  systematic review's caution that
  the implicated minerals may be covariates rather than causes is quoted
  directly, because this entry names specific minerals and should not assert
  more than its sources do.

  The exposure is DERMAL, and it is recorded in `exposure_classifications`
  rather than only in prose. Among the KB entries that carry that block, the
  mineral-dust diseases - silicosis, coal workers' pneumoconiosis and asbestosis
  - all record INHALATION, so podoconiosis is the transdermal member of that
  set. Two things that would make a stronger claim false, and are worth stating:
  `Byssinosis` is classified BIOLOGICAL rather than as a mineral dust, and
  `Chronic_Beryllium_Disease` curates a "Dermal beryllium exposure" entry of its
  own - it simply has no `exposure_classifications` block, so it does not appear
  in the comparison.

  Not curated. The deep-research report describes depression and anxiety odds
  ratios, quality-of-life subdomain scores, economic burden figures, a
  standardized mortality ratio of about 6, and a Rwandan barefoot-walking ban.
  These trace to sources this session did not fetch, so none is included. The
  report also suggested three UBERON terms its own validator flagged as naming
  something else - `UBERON:0002387` for dermis (it is *pes*), `UBERON:0004357`
  for dorsum of foot (*paired limb/fin bud*), and `UBERON:0001511` for "leg
  structures" (*skin of leg*) - plus `UBERON:0002391` for lymph node (*lymph*),
  which its weaker "worth a second look" section listed. None is bound as the
  report proposed it. `UBERON:0001511` *is* used here, but for what UBERON
  actually calls it: the skin of the leg.

📚

References & Deep Research

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Record notes

Why this entry exists. Podoconiosis is the cleanest gene-environment disease available: a mineral exposure with no pathogen and no vector, an HLA class II susceptibility replicated across three populations, and a heritability of 63% layered on an obligate environmental cause. Neither half produces disease alone - mineral particles are found in the lymph nodes of unaffected residents, and no genotype causes podoconiosis without the soil. Two things are curated as evidence rather than smoothed away. The in vitro mineral stimulation result runs against the obvious model and is kept with an explanation that says so and a discussion that argues it out. And the systematic review's caution that the implicated minerals may be covariates rather than causes is quoted directly, because this entry names specific minerals and should not assert more than its sources do. The exposure is DERMAL, and it is recorded in `exposure_classifications` rather than only in prose. Among the KB entries that carry that block, the mineral-dust diseases - silicosis, coal workers' pneumoconiosis and asbestosis - all record INHALATION, so podoconiosis is the transdermal member of that set. Two things that would make a stronger claim false, and are worth stating: `Byssinosis` is classified BIOLOGICAL rather than as a mineral dust, and `Chronic_Beryllium_Disease` curates a "Dermal beryllium exposure" entry of its own - it simply has no `exposure_classifications` block, so it does not appear in the comparison. Not curated. The deep-research report describes depression and anxiety odds ratios, quality-of-life subdomain scores, economic burden figures, a standardized mortality ratio of about 6, and a Rwandan barefoot-walking ban. These trace to sources this session did not fetch, so none is included. The report also suggested three UBERON terms its own validator flagged as naming something else - `UBERON:0002387` for dermis (it is *pes*), `UBERON:0004357` for dorsum of foot (*paired limb/fin bud*), and `UBERON:0001511` for "leg structures" (*skin of leg*) - plus `UBERON:0002391` for lymph node (*lymph*), which its weaker "worth a second look" section listed. None is bound as the report proposed it. `UBERON:0001511` *is* used here, but for what UBERON actually calls it: the skin of the leg.

Create: Podoconiosis (MONDO:0005425) · 2026-09-07T04:08:27Z · View source

Create the Podoconiosis entry (MONDO:0005425), a new curation with an environmental-exposure focus requested by the user. Claim issue #11296. Why this disease. Podoconiosis is the cleanest gene-environment disease available in the neglected-tropical-disease space: no pathogen, no vector, a mineral exposure through the skin, and an HLA class II susceptibility with 63% heritability layered on an obligate environmental cause. It exercises `environmental:` and `influences_mechanisms`, which most entries leave empty. Preflight was clean on all three surfaces - no entry, no stub, no open or closed issue or PR. Deep research. Requested as `falcon` per the skill default; no EDISON_API_KEY is configured here, so the run used `--fallback` and the report records `fell_back: true`, `requested_provider: falcon` and the ProviderNotConfiguredError, renamed to `-claude_code` on completion. 41/41 references resolved, 0 confabulation, 1 flagged off topic (PMC:PMC1008352, not cited). Term validation resolved 24/24 and flagged four bindings the report named wrongly: UBERON:0002387 (*pes*, not dermis), UBERON:0004357 (*paired limb/fin bud*, not dorsum of foot) and UBERON:0001511 (*skin of leg*, not "leg structures") in its "names something else" section, plus UBERON:0002391 (*lymph*, not lymph node) in its weaker "worth a second look" section. None is bound as the report proposed it; UBERON:0001511 is used, but for what UBERON actually calls it. Note the sequencing: `just research-disorder` requires the disorder file to exist, so a minimal schema-valid scaffold was written first and then replaced. Pathophysiology. Thirteen nodes, one root, no orphans. Barefoot soil contact -> transdermal particle entry -> macrophage phagocytosis -> lymphatic transport, which forks into an HLA-restricted arm and a direct particle effect on the vessel wall, both converging on endolymphangitis -> collagenization -> luminal obliteration -> lymph stasis -> dermal sclerosis -> epidermal barrier failure -> acute dermatolymphangioadenitis, which feeds back into collagenization. The feedback edge makes the graph cyclic, which is how the clinical literature describes it. Three findings curated as negatives or contradictions rather than smoothed away: - PMID:39591258 found that on stimulation with kaolinite and chlorite it was the healthy endemic controls, not the patients, who produced two to three times more IL-1beta - the opposite of a hypersensitivity model. Curated with an explanation that says so plainly and an INTERPRETATION discussion. - PMID:22455414 states that mineral particles are found in the lymph nodes of unaffected as well as affected people. Curated on the phagocytosis node, because it is the reason the HLA node exists at all. - PMID:25401490 found HPV-PCR negative in every specimen, ruling out the obvious alternative explanation for the verrucous change. Where the entry declines to assert more than its sources. The systematic review that assembles the implicated minerals (PMID:40623043) says outright they may be covariates rather than direct contributors; that sentence is quoted. The edge from particle transport to the HLA node is INDIRECT_UNKNOWN_INTERMEDIATES, not "antigen presentation", because how a silicate engages class II is unsolved - recorded as a KNOWLEDGE_GAP. PRE-PR RED-TEAM REVIEW. A subagent review against `dismech-pr-review` before any PR was opened returned REQUEST_CHANGES with seven blocking findings. All were verified against the caches and all were fixed. The substantive ones: 1. The stated diagnostic discriminator - "ascending", "spares the groin", and "descending/unilateral" for filariasis - appeared in five places including a `diagnostic: true` phenotype, and NO cited source supported any of it. It traced to the deep-research report, which is a lead and not a citable source. Rewritten to what the sources do say: "starting from the feet, progressively involving the legs, yet in most cases remaining below the knee" (PMID:35604949), bilateral in 86.9%, above the knee in 1.4%, asymmetric in stage (36%) and type (18.5%). The filariasis distinction is now the real, citable one - proximal worm nests versus distal soil exposure (PMID:33348721) - which is mechanistically better than the clinical rule of thumb it replaced. 2. `VERY_FREQUENT` on acute dermatolymphangioadenitis was justified by an episode rate (23.9 per person-year), not the patient proportion the enum band is defined on. Retagged FREQUENT against the 38% of the control arm reporting any attack (PMID:33348721), with the rate kept and relabelled. 3. Three false claims about repository state, all verified false and all fixed: (a) the notes claimed podoconiosis is the only DERMAL exposure among the KB's mineral-particle diseases. `Chronic_Beryllium_Disease` has no `exposure_classifications` at all and curates a "Dermal beryllium exposure" entry; `Byssinosis` is classified BIOLOGICAL; `Asbestosis` was omitted from the list. Rewritten to a claim that is true and states both exceptions. (b) the notes mislisted which UBERON terms the report's validator flagged and in which section - corrected above. (c) "All three are bound on the pathophysiology node" while only two genes were bound. HLA-DQB1 (hgnc:4944) is now bound. 4. The Ankle Ankylosis phenotype carried no evidence, justified by the claim that the staging description "was not available as a quotable cached reference". False - PMID_35604949 carries a figure legend placing ankylosis in stage 5 verbatim, and stage descriptions for 1, 2, 4 and 5. All are now cited, and stage 3 carries an explicit note saying why it has none. 5. `supports: REFUTE` on the HPV finding was inverted: `supports` is relative to the record it sits on, and the record asserts the change is NOT HPV-driven, which the negative PCR supports. Regraded SUPPORT. The same reasoning regraded the inverted IL-1beta item from REFUTE to SUPPORT. 6. The skin node bound `UBERON:0002067` *dermis* under a broader `preferred_term`, and excluded the node's own headline epidermal finding. Rebound to `UBERON:0001511` *skin of leg*. 7. The Endolymphangitis node rested solely on rabbit data. Human evidence added (PMID:25401490 infiltrate; PMID:38448477 for the endolymphangitis description, graded OTHER/INDIRECT since it summarises Price's work). Also from the review: three bundled nodes were split (phagocytosis vs transport, collagenization vs obliteration, dermal sclerosis vs epidermal barrier failure); the CD4 node was retagged CELLULAR; six evidence items citing narrative-review summary text or background prose were regraded HUMAN_CLINICAL -> OTHER with corrected explanations; `clinical_trials:` was added for both RCTs via their WHO ICTRP registrations (ISRCTN67805210 and ISRCTN16764792, both fetched with `just ictrp-fetch`); an `inheritance:` block was added; and the footwear treatment's "halt or reverse" claim gained the sentence that actually says it (PMID:35604949, stages 1 and 2 completely reversible). One inheritance-term judgment: `HP:0032113` *Semidominant inheritance* matches the segregation analysis's "autosomal co-dominant" wording, but it sits under *Mendelian inheritance* in HPO, and podoconiosis produces no disease without the exposure. Bound `HP:0001426` *Non-Mendelian inheritance* instead and recorded the reasoning in the block description. No term beats a bad one. Datasets: none added. `just discover-datasets Podoconiosis` returned exactly one candidate, geo:GSE119367, tagged GENE_ONLY - a leprosy GWAS in a Chinese Han population reached through HLA-DQA1. That is Named Entity Confusion reached via dataset search, and it was rejected on relevance. GeneReviews: none exists; confirmed by PubMed search. Podoconiosis is a complex gene-environment trait, not a Mendelian disorder. Animal model: the intralymphatic silica injection experiment (PMID:3006293) with three typed divergences, including a POPULATION_MISMATCH marked INVALIDATING - the animals are unselected, so the model cannot speak to the susceptibility step. Species is Rabbit, from the record's MeSH indexing; the abstract says only "animal experiments", and the entry says so. A HUMAN_MODEL_MISMATCH discussion records that no model can reproduce a disease requiring both a human HLA haplotype and barefoot bipedal soil contact. One term was invented and caught by validation: NCIT:C15311 was written for "Preventive Intervention" and is actually *Quality Control*. Corrected to NCIT:C15843. Not curated: the report's depression and anxiety odds ratios, quality-of-life scores, economic burden figures, standardized mortality ratio, OMIM 614590 mapping, and the Rwandan barefoot-walking ban all trace to sources this session did not fetch. Recorded in `notes:` rather than included. Validation after the review round: `just validate-disorders` clean, 96/96 snippets verified, term validation passed, entity refs / causal targets / duplicate keys / enum values / qualifier terms / source-defect claims all OK, pathograph re-audited (13 nodes, one root, no orphans), `just compliance` 81.9%. Cache diff is additions only. 30 uncited reference caches written by the report's own validation pass were pruned, the cited list re-derived immediately afterwards, and the snippet count re-run on the pruned tree. Every reference_title was derived programmatically from references_cache frontmatter rather than typed.

Claude Code ▸

Podoconiosis (Endemic Non-Filarial Elephantiasis / Geochemical Lymphedema): Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 43 citations 2026-09-07T03:33:39.186159

Podoconiosis (Endemic Non-Filarial Elephantiasis / Geochemical Lymphedema): Comprehensive Research Report

1. Disease Information

Overview. Podoconiosis (also "podoconiosis," from Greek podos [foot] + konia [dust]) is a non-infectious, geochemical lymphedema of the lower legs caused by long-term contact of bare feet with irritant, mineral-rich red clay soils derived from alkalic volcanic rock, occurring exclusively in genetically susceptible individuals. It is the second most common cause of tropical lymphedema worldwide after lymphatic filariasis and is one of the very few WHO Neglected Tropical Diseases (NTDs) that is non-infectious — grouped, unusually, with snakebite envenoming in the "non-infectious NTD" category of the WHO 2021–2030 NTD roadmap. It is also known by the regional lay term "mossy foot" for its hyperkeratotic, moss-like papillomatous skin lesions.

Key identifiers: - MONDO: MONDO:0005425 - OMIM: 614590 — "PODOCONIOSIS, SUSCEPTIBILITY TO; PDCOS" (susceptibility locus entry, not a classic Mendelian disease entry) - Disease Ontology: DOID:0050138 - MeSH: D062846 ("Elephantiasis, Nonfilarial" / historically indexed with "Non-Filarial Lymphedema") - ICD-10/ICD-11: no dedicated podoconiosis-specific code was identified in this search; it is typically coded under non-filarial lymphedema/elephantiasis categories (curators should verify current ICD-11 foundation entries directly before binding). - An Orphanet (ORPHA) code was not confirmed via this search and should be checked directly against Orphadata before citing.

Synonyms: endemic non-filarial elephantiasis; nonfilarial elephantiasis; tropical non-filarial elephantiasis; geochemical elephantiasis; "mossy foot" disease; podoconiosis lymphoedema.

Data provenance: The evidence base is overwhelmingly aggregated, disease-level (cross-sectional community surveys, case-control studies, disease registries such as the Ethiopian national podoconiosis mapping, and genetic-epidemiology cohorts from southern Ethiopia), rather than individual EHR-derived data — reflecting its concentration in resource-limited rural settings without electronic health infrastructure. (WHO fact sheet; Deribe et al., PLoS NTD "Ten Years of Podoconiosis Research in Ethiopia," 2013.)

2. Etiology

Disease causal factors — a gene–environment disease model. Podoconiosis is the paradigm example of a disease requiring both a specific environmental exposure (chronic bare-foot contact with irritant volcanic soil) and genetic susceptibility (HLA class II variants); neither alone is sufficient. The WHO states: "evidence suggests that podoconiosis is the result of a genetically determined abnormal inflammatory reaction to mineral particles in irritant red clay soils derived from volcanic deposits." No infectious agent has ever been identified despite extensive investigation.

Genetic risk factors: - HLA class II locus (chromosome 6p21.3): The first genome-wide association study (GWAS) of podoconiosis (Tekola Ayele F, et al., N Engl J Med 2012;366:1200-8; PMID:22455414) genotyped 194 cases and 203 controls from southern Ethiopia and found genome-wide significant association with rs17612858 (OR 2.19; P=3.44×10⁻⁸), an intergenic SNP between HLA-DQA1 and HLA-DQB1, plus seven other genome-wide-suggestive SNPs in the HLA class II region. Together the HLA SNPs explained ~15.6% of genetic variance and conferred a 2–3-fold increase in risk. - Replication: A follow-up study (Sci Rep 2021;11:2941; PMID:33558538) replicated HLA class II (DRB1, DQA1, DQB1) association across three Ethiopian ethnic groups (Wolaita, Amhara, Oromo), strengthening the causal case beyond a single population. - Heritability/segregation analysis: Multi-generational family studies in the Wolaita ethnic group (1,400 individuals across 59 families) found a sibling recurrence risk ratio (λs) of 5.07 and heritability of 0.63, with the best-fitting model being an autosomal co-dominant major gene, with age and footwear use as significant environmental covariates (Davey G, et al., genetic epidemiology studies referenced in Trans R Soc Trop Med Hyg / PLoS NTD, Ethiopia). - Mechanistic immunogenetic follow-up: Because HLA class II presents peptide antigens to CD4+ T cells, the HLA association implicates podoconiosis as a T-cell-mediated inflammatory disease. A 2020 multiplexed gene-expression study (PMC7738654) and a 2024 Nature Communications paper ("Evidence for immune activation in pathogenesis of the HLA class II associated disease, podoconiosis," PMCID PMC10917762 — PMID not independently confirmed in this search and should be verified before citation) both report signatures of chronic immune activation consistent with an antigen-driven, T-cell-mediated response to mineral particles.

Environmental/exposure risk factors: - Soil composition: Weathering of basaltic and alkaline volcanic rock produces red clay soils rich in smectite and kaolinite clays, mica-group minerals, crystalline silica (quartz), iron oxide, and zirconium; WHO also implicates aluminium and beryllium. A 2023 geochemical/mineralogical characterization study (PMC10611848) and a 2017 study on the haemolytic activity of soils from areas of varying podoconiosis endemicity (PLoS ONE 2017; PMC5426718) both link specific mineral/geochemical profiles to endemicity gradients. - Barefoot exposure duration: Duration and age of onset of barefoot exposure are the dominant environmental determinants; age of first shoe-wearing correlates positively with age of podoconiosis onset. - Occupation: subsistence farming with prolonged barefoot contact with cultivated volcanic soils is the classic occupational exposure. - Altitude: endemic zones are characteristically high-altitude areas with volcanic soils (contrasting with lymphatic filariasis, which is a low-lying, mosquito-borne disease). - Socioeconomic status: extreme rural poverty precluding shoe ownership is a structural risk factor.

Protective factors: - Consistent footwear use is the principal, well-established environmental protective factor across multiple case-control studies (e.g., Rwanda: "none of the controls went barefoot… in contrast to 11.6% of controls, none of the patients wore closed shoes," Musanze District case-control study, PMC13497288). Floor covering in homes (reducing indoor soil contact) is also protective. - Foot hygiene (regular washing) reduces cumulative mineral-particle penetration. - No specific protective genetic variant/allele has yet been robustly identified (absence of the risk HLA haplotypes is implicitly protective, but no independent protective locus has been reported in the searched literature).

Gene–environment interaction. Podoconiosis is repeatedly cited in the literature as a "tropical model for gene–environment interactions" (Davey G, Trans R Soc Trop Med Hyg, 2006) — disease develops only in the intersection of (a) sustained soil exposure and (b) HLA class II susceptibility genotype; neither factor alone produces disease, and community understanding studies show that ~59% of Ethiopian youth in endemic areas already correctly conceptualize this joint causation (PMC6155534).

3. Phenotypes

Podoconiosis exhibits a well-characterized clinical progression from early reversible inflammatory changes to fixed fibrotic elephantiasis. A de novo five-stage clinical staging system (Tekola F, et al.) is the field standard:

Stage	Features
1 (early)	Itching, tingling/burning sensation on the dorsum of the foot, mild forefoot widening, intermittent swelling
2	"Water-bag" pitting, soft edema; flask-shaped leg (narrow at knee, wide at ankle); smooth, dumpy foot surface
3	Fibrotic, non-pitting edema below the knee; sclerotic hyper-/hypopigmentation on the shin; fibrotic ridge at the flexural ankle; early nodules, plantar involvement
4 (advanced)	Non-pitting edema extending above the knee; skin depigmentation around the ankle
5 (advanced)	Fibrotic, globular, "woody"/rubbery tumor-like swelling; ankle ankylosis; multiple nodules and scarring; band-like redundant "pillowy" skin folds

Symptoms/signs by category: - Cutaneous: hyperkeratotic, "mossy," papillomatous nodules (moss-like lesions present in ~77.5% of patients, often bilateral); dry, thickened, fissured skin; toe maceration; plantar/dorsal nodules; hyper- and hypopigmentation. - Lymphedema: chronic, bilateral but asymmetric, ascending (rather than descending) leg swelling that typically spares the groin — a key distinguishing feature from filarial lymphedema. - Musculoskeletal: ankle ankylosis and joint fixation in advanced (stage 4–5) disease, causing significant mobility impairment. - Systemic/complication phenotype — Acute dermatolymphangioadenitis (ADLA): recurrent acute attacks of fever, pain, erythema, and worsening swelling, triggered by bacterial entry through fissured/cracked skin. Patients experience on average ≥5 episodes/year (up to 23.3/year reported in one Ethiopian district), totaling ~90 incapacitated days/year (PMC6638979; medRxiv 2025.05.12.25327479). Each ADLA episode drives further lymphatic damage and disease progression. - Laboratory/hematological: studies from West Gojjam, Ethiopia (PMC11687886) and Musanze, Rwanda (PMC13497288) report altered hematological and immunological profiles (e.g., elevated inflammatory markers) versus controls, though these are not yet incorporated into diagnostic criteria. - Behavioral/psychological: severe depression (OR ~19.8), anxiety (OR ~10.7), and stress symptoms (OR ~13.5) are markedly elevated versus unaffected neighbors (Rwanda comparative study, PLoS NTD 2024, PMC11309478/PMID 39116063); depressive-symptom prevalence reported at 12.6% (Ethiopia), 38.5% (Cameroon), and 68.5% (Rwanda) among patients.

Phenotype characteristics: - Onset: insidious, typically in young adulthood — mean age at first noticing leg swelling ≈ 25 years; onset is rare before age 5–6, rises through adolescence, and can present up to the sixth decade or later. - Progression: chronic, slowly progressive over years to decades if unmanaged; early stages (1–2) are reversible with footwear and hygiene, but stages 3–5 involve fixed fibrosis. - Severity/frequency: variable; frequency of nodular/hyperkeratotic ("mossy") lesions ~77.5%; in Ethiopian endemic districts prevalence of any stage disease reaches 5–10%. - Quality of life impact: significantly reduced across all four WHOQOL subdomains (physical, psychological, social, environmental) versus healthy controls (Northern Ethiopia QOL study, PMC3726315); stigma, illiteracy, comorbidity, and being unmarried are independent correlates of poor QOL.

Suggested HPO terms (leads only — must be verified against the current HPO release before curation, per dismech's anti-hallucination policy): - Lower-limb lymphedema / lymphedema (general lymphedema term) - Hyperkeratosis (HP:0000962 general hyperkeratosis concept) - Skin ulcer / skin fissuring - Ankle contracture / joint ankylosis - Depression, Anxiety (as secondary/behavioral phenotypes) - Recurrent skin infections (as the substrate of ADLA)

4. Genetic/Molecular Information

Causal/susceptibility genes: Podoconiosis is not a single-gene Mendelian disorder; it is modeled as a complex, HLA class II-associated susceptibility trait (OMIM 614590, "PODOCONIOSIS, SUSCEPTIBILITY TO"). No monogenic causal mutation has been described.

Implicated loci/genes (HGNC where applicable): - HLA-DQA1 / HLA-DQB1 (intergenic SNP rs17612858 between them) — Tekola Ayele et al., PMID:22455414. - HLA-DRB1 — implicated in replication study (PMID:33558538) alongside DQA1/DQB1.

Variant classification: These are common-variant (population-frequency) susceptibility alleles identified by GWAS, not rare pathogenic Mendelian variants — so ACMG/AMP pathogenicity tiers do not directly apply. Effect sizes are modest (OR ~2.19 for the lead SNP), consistent with a polygenic/complex-trait architecture layered on an obligate environmental exposure.

Allele frequency: Population-level allele frequencies for the implicated HLA class II haplotypes in Ethiopian populations were reported in the original GWAS and replication studies but specific frequency values were not retrieved in this search; gnomAD/1000 Genomes do not have curated podoconiosis-specific frequency annotations (this is an HLA-region association, so standard biallelic-variant frequency databases are of limited direct use — HLA imputation/typing panels are more appropriate).

Somatic vs. germline: Exclusively germline susceptibility (host genetic background), acting in combination with an acquired environmental exposure — not a somatic disease.

Functional consequences: The HLA class II susceptibility association is interpreted as conferring an altered antigen-presentation profile that predisposes CD4+ T cells to mount a chronic, maladaptive inflammatory response to mineral particles absorbed through the skin — i.e., gain-of-function of a pathological adaptive immune response, not a loss-of-function protein defect.

Modifier genes: None specifically named beyond the co-dominant "major gene" inferred by segregation analysis; the field considers additional minor loci and environmental covariates (age, footwear) likely but not yet mapped.

Epigenetic information / chromosomal abnormalities: No epigenetic (DNA methylation, histone modification) studies or chromosomal-abnormality data specific to podoconiosis were identified in this search — this appears to be an open research gap.

Molecular/immunological profiling: - A 2020 multiplexed gene-expression (NanoString-type) study of PBMCs from HLA class II-genotyped cases/controls (PMC7738654) found evidence of chronic immune activation transcriptional signatures. - A 2024 Nature Communications study (PMC10917762) extended this, reporting immune-activation evidence directly tied to the HLA-associated disease mechanism. - A cytokine-stimulation study (PMC11598685) measured TNF-α, IL-1β, and IFN-γ by ELISA in PBMCs from cases vs. endemic healthy controls, at baseline and after in vitro stimulation with kaolinite, chlorite, and beryllium sulfate. Key finding: baseline (unstimulated) TNF-α and IL-1β were significantly higher in patients than controls, but after mineral stimulation, healthy controls showed a paradoxically greater increase in IL-1β (2–3-fold higher with kaolinite/chlorite) than patients — suggesting patients' cells may already be in a chronically activated/exhausted state at baseline. No significant difference in cytokine gene mRNA expression was found, though slight increases in IL-1β and TGF-β were noted.

5. Environmental Information

Environmental factors: The central environmental agent is chronic transdermal (plantar) exposure to irritant, alkalic-volcanic-derived red clay soil. Implicated mineral/chemical constituents (from soil geochemistry studies, PMC10611848 and PMC5426718): - Smectite and kaolinite clays (phyllosilicates) - Mica-group minerals - Crystalline silica/quartz (colloid-sized alumino-silicate particles) - Iron oxide - Zirconium - Aluminium and beryllium (per WHO)

Soils from higher-endemicity areas show measurably different mineralogical/geochemical and hemolytic-activity profiles compared to soils from lower-endemicity areas of the same region, supporting a soil-composition dose-response relationship.

Lifestyle factors: Habitual bare-footedness (occupational and cultural norm in affected rural communities); lack of floor coverings in homes; poverty precluding shoe purchase/replacement.

Infectious agents: None causally implicated in the primary disease process (podoconiosis is explicitly non-infectious). However, secondary bacterial infection through fissured, hyperkeratotic skin is the proximate trigger for ADLA attacks, which drive disease exacerbation; a 2023 study (Sci Rep 2023, "Tropical leg lymphedema caused by podoconiosis is associated with increased colonisation by anaerobic bacteria") found increased anaerobic bacterial colonization of affected limbs, implicating a polymicrobial (largely anaerobic) skin/soft-tissue flora in the acute-attack pathophysiology.

6. Mechanism / Pathophysiology

Causal chain (numbered, with inference status noted)

Chronic barefoot contact with alkalic-volcanic-derived red clay soil exposes plantar/dorsal foot skin to colloid-sized alumino-silicate mineral particles (kaolinite, smectite, quartz/silica, zirconium, aluminium, beryllium) over years. (Demonstrated — epidemiological and geochemical studies.)
This exposure leads to transdermal/transcutaneous penetration of ultrafine mineral particles into the dermis and subcutaneous lymphatics — inferred from post-mortem/biopsy microanalysis showing intralysosomal silicon and aluminium in macrophages of affected lymphatics and lymph nodes (Price-era histochemical studies; Trans R Soc Trop Med Hyg 1985 lymph node/vessel silica study). (Demonstrated in human tissue and supported by animal intralymphatic-silica injection experiments — see below.)
In HLA class II-susceptible individuals (particularly those carrying risk alleles/haplotypes at HLA-DQA1/DQB1/DRB1), this leads to an aberrant, sustained CD4+ T-cell-mediated adaptive immune response against the mineral particles/particle-associated antigens, rather than normal clearance. (Inferred from GWAS + immune-activation transcriptomic studies; the precise antigenic mechanism by which minerals engage HLA class II presentation is not directly demonstrated and remains a key open question.)
Mineral particles are phagocytosed by macrophages in the dermal lymphatics and regional lymph nodes; intralysosomal accumulation results in lysosomal membrane rupture, macrophage destruction/activation, and release of pro-fibrotic and pro-inflammatory mediators. (Demonstrated — histopathology and the classic silica-macrophage cytotoxicity model, analogous to silicosis pathogenesis.)
Chronic macrophage activation and cytokine release (elevated baseline TNF-α, IL-1β; likely TGF-β involvement) drive endolymphangitis — inflammation of the lymphatic vessel wall — with recruitment of mast cells, lymphocytes, and plasma cells (biopsy series: 94% mast-cell infiltration, 71% plasma-cell infiltration, plus papillary/reticular dermal lymphocytic infiltrate). (Demonstrated by histopathology, PMID:35604949.)
Persistent endolymphangitis causes progressive collagen deposition and fibrosis within lymphatic vessel walls and surrounding dermis (thickened, vertically arranged papillary-dermal collagen bundles; horizontally arranged reticular-dermal bundles; media-sclerosis of blood vessels in later stages). (Demonstrated.)
Fibrotic thickening and scarring of the lymphatic wall result in obliteration of the lymphatic lumen and mechanical obstruction to lymph flow — the direct structural lesion producing lymphedema. (Demonstrated — lymphographic and histologic evidence; note early Price-era experiments found silica's obstructive effect on lymph vessels themselves exceeded its effect via lymph nodes.)
Lymphatic obstruction leads to chronic interstitial fluid accumulation in the foot/lower leg (clinical edema, initially reversible/pitting — clinical stages 1–2). (Demonstrated.)
Ongoing lymph stasis and tissue hypoxia drive progressive dermal/subcutaneous fibrosis, hyperkeratosis, and papillomatosis, producing the fixed, non-pitting, "mossy," nodular elephantiasis of advanced stages 3–5, including ankle ankylosis from peri-articular fibrosis. (Demonstrated clinically/histologically; the precise molecular fibrogenic pathway — e.g., specific TGF-β/fibroblast activation signaling — is inferred by analogy to other fibrotic lymphedemas rather than directly dissected in podoconiosis-specific mechanistic studies.)
Branch — acute exacerbation loop: Chronic skin fissuring/hyperkeratosis (from step 9) creates portals of entry for skin flora (including anaerobic bacteria); bacterial invasion triggers recurrent ADLA attacks (fever, erythema, acute swelling), each of which further damages lymphatic architecture and accelerates progression back into step 6–9, creating a self-reinforcing cycle of episodic acute inflammation superimposed on chronic fibrosis. (Demonstrated epidemiologically and microbiologically; the precise host-microbe interaction is inferred.)

Detail by mechanism category

Molecular pathways: No podoconiosis-specific signaling pathway (e.g., a defined Wnt/MAPK/PI3K-AKT cascade) has been directly dissected; the field relies on general models of particulate-induced macrophage activation (analogous to silicosis) and T-cell/HLA antigen-presentation biology. Candidate GO terms: positive regulation of NF-kappaB transcription factor activity, T cell receptor signaling pathway, inflammatory response.
Cellular processes: macrophage phagocytosis and lysosomal rupture; T-cell activation; mast-cell and plasma-cell infiltration; fibroblast activation/collagen synthesis; endothelial injury to lymphatic vessel walls.
Protein dysfunction: No specific misfolded/aggregating protein is implicated; the "dysfunction" is at the level of an aberrant HLA class II-restricted immune recognition event rather than an intrinsic protein structural defect.
Metabolic changes: Not specifically characterized in the literature reviewed.
Immune system involvement: Central — chronic, HLA class II-restricted, T-cell-mediated inflammatory/autoinflammatory-like response; elevated baseline pro-inflammatory cytokines (TNF-α, IL-1β); mast cell and plasma cell tissue infiltration; blunted mineral-specific cytokine response in patients relative to healthy exposed controls, suggesting immune exhaustion/dysregulation rather than simple hyperreactivity.
Tissue damage mechanisms: silica/mineral-induced macrophage cytotoxicity, chronic lymphangitis, fibrosis, and secondary infection-driven acute tissue injury (ADLA).
Biochemical abnormalities: No specific enzyme deficiency or ion-channel defect; the defect is immunogenetic (HLA-restricted antigen presentation) rather than a classical inborn-error biochemical lesion.
Epigenetic changes: Not characterized in the literature surveyed — an open research gap.
Molecular profiling: Transcriptomic (gene-expression) data exist (PMC7738654, PMC10917762) showing immune-activation signatures; no proteomics, metabolomics, or lipidomics datasets specific to podoconiosis were identified.
Advanced technologies: No single-cell, spatial transcriptomic, multi-omics, or CRISPR/RNAi functional-genomics studies of podoconiosis were found in this search — likely reflecting the disease's neglected status and resource-limited research settings.

Suggested GO terms (leads, to be verified): GO:0006955 (immune response), GO:0002250 (adaptive immune response), GO:0030198 (extracellular matrix organization), GO:0042060 (wound healing), GO:0002437 (inflammatory response to antigenic stimulus). Suggested CL terms (leads): CL:0000235 (macrophage), CL:0000097 (mast cell), CL:0000542 (lymphocyte), CL:0000084 (T cell), CL:0000786 (plasma cell), CL:0000057 (fibroblast), CL:0002138 (endothelial cell of lymphatic vessel).

7. Anatomical Structures Affected

Organ level: Primary target is the lymphatic vasculature of the lower limb (dermal and subcutaneous lymphatics of the foot and leg below the knee, extending above the knee in advanced disease). Regional lymph nodes (inguinal typically spared/less involved than in filariasis) may show reactive/fibrotic change. Skin and subcutaneous tissue of the foot/leg are secondarily and prominently affected (integumentary system). No visceral organ involvement is described — this contrasts with filarial disease, which can involve genital/scrotal lymphatics.
Body systems involved: lymphatic system (primary); integumentary system (skin — hyperkeratosis, fibrosis, nodules); musculoskeletal system (secondary — ankle joint ankylosis in advanced stages); immune system (T-cell/HLA-mediated pathogenesis).
Tissue/cell level: dermal papillary and reticular connective tissue (fibrosis); lymphatic endothelium; macrophages, mast cells, lymphocytes, and plasma cells within the dermis and perilymphatic tissue; eccrine sweat gland hyperplasia has also been described in advanced-stage biopsies.
Subcellular level: macrophage lysosomes/phagolysosomes are the key subcellular compartment — intralysosomal accumulation of silicon/aluminium mineral particles, lysosomal membrane rupture, and consequent release of pro-fibrotic mediators (candidate GO Cellular Component term: GO:0005764 lysosome).
Localization: bilateral but asymmetric, ascending distribution beginning at the foot/ankle and progressing proximally; characteristically spares the groin/genitalia (unlike filarial lymphedema). Suggested UBERON terms: UBERON:0002387 (dermis), UBERON:0004357 (dorsum of foot) or UBERON:0002387/UBERON:0001511 (leg structures), UBERON:0001473 (lymphatic vessel), UBERON:0002391 (lymph node).

8. Temporal Development

Onset: insidious/chronic onset (not acute), typically in adolescence to young adulthood; mean age at first noticing swelling ≈25 years; can present from childhood through the sixth decade of life depending on exposure duration.
Progression: Five clinical stages (see Section 3) representing a continuum from early reversible pitting edema (stages 1–2) to fixed fibrotic elephantiasis with joint ankylosis (stages 4–5). Progression rate is variable and strongly modifiable by intervention — footwear/hygiene adoption can halt or reverse early-stage disease, while established fibrosis (stage 3+) is largely irreversible.
Disease course pattern: chronic and progressive at baseline, but punctuated by recurrent acute exacerbations (ADLA) that produce an episodic/relapsing component superimposed on the underlying progressive fibrotic course; disease is lifelong without effective self-care.
Remission: partial "remission" (reduction in edema/symptom burden) is achievable with sustained conservative management (foot hygiene, compression, elevation, footwear) especially in early stages; spontaneous remission does not occur.
Critical periods: early childhood is a critical window for prevention (early and consistent shoe adoption is strongly associated with delayed or prevented onset); once fibrosis is established, the window for reversal closes, making early intervention the key modifiable period.

9. Inheritance and Population

Epidemiology: - Global burden: ~4 million people affected worldwide, with disease potential in 32 countries (18 in Africa, 3 in Asia, 11 in Latin America); the WHO fact sheet cites ~17 countries with confirmed cases (12 African, 3 Latin American, 2 Asian) — reflecting the gap between "potentially endemic" and "confirmed endemic" counts. Podoconiosis is not yet incorporated into the Global Burden of Disease (GBD) study, a recognized evidence gap, and most quantitative prevalence data originate from Ethiopia specifically. - Ethiopia: bears an estimated ~25% of the global burden; >35 million people at risk across 345 endemic districts; >1.5 million people (some sources: 1.6 million) living with the disease. Ethiopia-specific pooled prevalence (meta-analysis) = 4.52% (95% CI 3.92–5.16%); in specific endemic districts, prevalence reaches 5–10%. - Burden metrics: 172,073 DALYs annually in Ethiopia (182 per 100,000 population, 2017 estimate); total annual economic burden in Ethiopia estimated at US$213.2 million, of which 91.1% is productivity loss; an older (2004) estimate cited ~US$200 million annual productivity loss. - Mortality: a standardized mortality ratio of ~6 has been reported among affected populations (WHO), though podoconiosis itself is not directly fatal — excess mortality likely reflects ADLA sepsis risk, disability-associated comorbidity, and reduced healthcare access.

Inheritance pattern: best-fit segregation model is autosomal co-dominant major-gene inheritance with significant environmental covariates (age, footwear) — i.e., a complex trait with a strong single-locus (HLA class II region) contribution layered on an obligate environmental exposure, rather than classic simple Mendelian inheritance.

Penetrance: incomplete and exposure-dependent — genetic susceptibility (HLA risk genotype) is necessary but not sufficient; penetrance requires the environmental exposure (chronic barefoot soil contact), making this a gene-by-environment-dependent penetrance model.

Heritability: h² = 0.63 (Wolaita family study); sibling recurrence risk ratio λs = 5.07.

Genetic anticipation, germline mosaicism, founder effects: not described/applicable — this is a common-variant, complex-trait susceptibility disease, not a repeat-expansion or classic single-gene disorder.

Consanguinity role: not specifically implicated as a risk modifier in the literature surveyed (contrasts with classic autosomal recessive disorders).

Carrier frequency: not meaningfully defined for a complex-trait/HLA-association disease in the way it is for a recessive Mendelian disorder.

Population demographics: - Affected populations: predominantly rural, subsistence-farming communities in East African highlands (Ethiopia, Uganda, Tanzania, Kenya, Rwanda, Burundi, Sudan/South Sudan, Cameroon) plus described foci in Central America and northern India. - Geographic distribution: endemic to high-altitude volcanic soil regions — a striking contrast to the low-lying, mosquito-vector-dependent distribution of lymphatic filariasis. - Sex ratio: conflicting across studies — a meta-analysis found women ~1.15× more likely affected than men; some single-site studies report much stronger female predominance (up to 3.2:1 in some regions), while a Wolaita, Ethiopia survey found near-parity (M:F ≈ 1:0.98), likely reflecting differing occupational/exposure patterns by locality. - Age distribution: most cases (~64%) occur in the economically productive 16–45-year age range; rare before age 5–6; some studies report highest prevalence after age 45–55, consistent with cumulative lifetime soil exposure.

10. Diagnostics

Diagnostic approach: Podoconiosis is fundamentally a diagnosis of clinical exclusion, based on history (barefoot residence in an endemic volcanic-soil area), physical examination (bilateral, asymmetric, ascending, groin-sparing lymphedema with characteristic mossy/nodular skin changes), and targeted tests to exclude the principal differential diagnoses.

Key differentiation from lymphatic filariasis (the most important differential):

Feature	Podoconiosis	Lymphatic filariasis
Laterality	Bilateral, asymmetric	Typically unilateral
Progression direction	Ascending	Descending
Groin/genital involvement	Very rare	Frequent (hydrocele common)
Geography	High-altitude volcanic soil	Low-lying, mosquito-endemic
Systemic febrile inflammatory episodes	ADLA (secondary bacterial)	Filarial adenolymphangitis
Filarial antigen test (ICT card)	Negative	Positive
Night blood smear microfilariae	Absent	Present (nocturnal periodicity in most regions)

Clinical/laboratory tests: - Filarial antigen rapid tests (e.g., ICT card test for circulating filarial antigen) and night blood smears for microfilariae are the standard exclusionary tests — negative in podoconiosis. - Ultrasound can detect the pathognomonic "filarial dance sign" of live adult worms in lymphatics in filariasis; its absence supports podoconiosis, though ultrasound is not itself diagnostic of podoconiosis. - Skin biopsy/histopathology (as in the PMC9166354/PMID:35604949 study) can support diagnosis by showing the characteristic papillary dermal lymphocytic infiltrate, mast-cell/plasma-cell infiltration, and collagen bundle changes, though this is a research rather than routine clinical tool. - No podoconiosis-specific serum biomarker or genetic test is in clinical use; the HLA class II association is a research finding, not (yet) a diagnostic test.

Differential diagnosis (beyond filariasis): lepromatous leprosy (distinguished by sensory loss, thickened peripheral nerves, trophic ulcers — absent in podoconiosis), Kaposi sarcoma, mycetoma pedis, elephantiasis nostras verrucosa (chronic venous/lymphatic disease from other causes), and systemic causes of lower-limb edema (e.g., cardiac, renal, hepatic).

Genetic testing: No clinical genetic test panel exists for podoconiosis; genetic/HLA typing remains a research tool (e.g., ClinicalTrials.gov NCT01939431, "Genetic and Other Aspects of Podoconiosis").

Screening: No formal population screening program beyond community-based case-finding/mapping surveys (e.g., Ethiopia's national integrated LF/podoconiosis morbidity mapping, PMC6044548) used to define endemic districts for targeted intervention.

11. Outcome/Prognosis

Mortality: Podoconiosis is not itself directly lethal, but a standardized mortality ratio of ~6 has been reported in affected populations (WHO), likely reflecting ADLA-related sepsis, disability-associated vulnerability, and healthcare-access disparities; formal disease-specific mortality/survival statistics (5-/10-year survival) are not established the way they are for cancers.
Morbidity/disability: Substantial — advanced-stage disease causes major functional impairment (mobility limitation from ankle ankylosis and massive limb swelling), lost productivity (91% of Ethiopia's US$213.2M annual economic burden is productivity loss), and profound social/psychological morbidity (severe depression OR ~19.8, anxiety OR ~10.7 versus unaffected neighbors).
Quality of life: significantly reduced across physical, psychological, social, and environmental WHOQOL domains; stigma (social exclusion from schools, churches, mosques, and marriage prospects) is a major independent driver of poor QOL, distinct from the physical disease burden itself.
Complications: recurrent ADLA (the dominant complication, causing ~90 incapacitated days/year in affected individuals in some cohorts); secondary bacterial/anaerobic infection; chronic wounds; joint ankylosis; disfiguring nodules.
Recovery potential: early-stage (1–2) disease is substantially reversible with consistent conservative management (footwear, hygiene, compression, elevation); stages 3–5 fibrotic/ankylotic changes are largely irreversible, though ADLA frequency and QOL can still be improved by treatment (nodulectomy, compression, hygiene) even in advanced disease.
Prognostic factors: stage at initiation of treatment, consistency of self-care/footwear adherence, frequency of ADLA episodes, and presence of stigma/psychosocial comorbidity all predict functional and QOL outcomes. No molecular/biomarker-based prognostic tool has been validated.

12. Treatment

There is no curative pharmacotherapy or disease-modifying drug for podoconiosis; management is centered on lymphedema self-care and, where needed, surgery — analogous to management of other chronic lymphedemas.

Supportive/conservative care (mainstay, evidence-based via RCT): - Foot hygiene: daily washing with soap, water, and antiseptic. - Emollients: regular application to reduce skin fissuring (a key ADLA-prevention measure). - Compression bandaging/garments and limb elevation at night. - Exercise and consistent use of socks and shoes. - This bundled regimen was tested in the GoLBeT trial ("Gojjam Lymphoedema Best Practice Trial," a pragmatic RCT in northern Ethiopia; protocol PMC4504163, results PMC6562300) — a community-based package delivered via lay "Community Podoconiosis Agents," designed specifically to reduce the frequency of ADLA episodes. An earlier one-year follow-up study of a simplified lymphedema treatment regimen in southern Ethiopia (PLoS NTD 2010, PMC2994920) demonstrated effectiveness of this basic self-care package. - Cost-effectiveness/social-outcome analysis of community-based treatment in East Gojjam (PMC6808421) supports scaling this model.

Surgical/interventional: - Nodulectomy (surgical debulking of fibrotic nodules): performed under local anesthesia, wounds left to heal by secondary intention with compression bandaging. A study of surgical debulking in Ethiopia (PLoS NTD 2021; PMID:33481805) found nodulectomy produced significant DLQI (Dermatology Life Quality Index) improvement with no serious complications, supporting its use as a standard resource-appropriate procedure. Suggested NCIT term: NCIT:C15329 (Surgical Procedure); the treatment could also carry therapeutic_modality: SURGERY.

Pharmacotherapy: No specific disease-modifying drugs exist; antibiotic therapy is used for acute ADLA episodes (targeting the secondary bacterial/anaerobic skin infection) — suggested NCIT term NCIT:C258 (Antibiotic) or a specific agent-level CHEBI/NCIT binding once a specific regimen is identified from local guidelines.

Rehabilitation/psychosocial: psychosocial support and community reintegration efforts (addressing stigma) are increasingly recognized as necessary treatment-adjacent components given the disproportionate mental-health burden; NCIT candidate: NCIT:C15747 (Supportive Care).

Advanced therapeutics (gene therapy, cell therapy, RNA-based, immunotherapy): none reported or applicable — podoconiosis management remains entirely in the domain of lymphedema self-care and surgery; there is no oncologic/immunotherapeutic analog in the literature reviewed.

Experimental treatments: GoLBeT (RCT, completed, community lymphedema-management package) is the key trial identified; ClinicalTrials.gov NCT01939431 ("Genetic and Other Aspects of Podoconiosis") is a genetic/observational study rather than an interventional trial. No NCT-registered pharmacologic trials were identified in this search.

Treatment algorithms: Stage-based — early (1–2) disease emphasizes prevention/reversal via footwear+hygiene; established fibrotic disease (3–5) combines ongoing lymphedema self-care with nodulectomy for symptomatic nodules and ADLA-prevention bundles to arrest further deterioration.

13. Prevention

Prevention is the single most impactful intervention category for podoconiosis, given the absence of curative treatment.

Primary prevention: the cornerstone — consistent footwear use from early childhood, daily foot hygiene (washing), and floor covering in homes to reduce indoor soil contact. Multiple case-control studies (Rwanda, Ethiopia) confirm shoe-wearing as the dominant modifiable protective factor. Rwanda has implemented a national public barefoot-walking ban as an explicit public-health prevention policy (also targeting other soil-borne diseases).
Secondary prevention: early case detection (community mapping surveys) and early initiation of self-care before fibrotic (stage 3+) changes become established.
Tertiary prevention: ADLA-prevention bundles (hygiene, emollients, compression) to prevent complications/further disease progression in those already affected — this is the GoLBeT trial's explicit target outcome.
Immunization: not applicable — no infectious/vaccine-preventable component.
Screening programs: population-based community mapping (integrated with lymphatic filariasis morbidity mapping in Ethiopia, PMC6044548) is used to define endemic districts for targeted resource allocation, rather than individual diagnostic screening.
Genetic screening/counseling: not currently part of clinical practice; research studies (e.g., NCT01939431) note that genetic research itself faces stigma-related informed-consent challenges in affected communities (BMC Medical Ethics qualitative study, cited in search results), a notable ethical/implementation consideration for any future genetic counseling program.
Behavioral interventions: community health education (e.g., the Mossy Foot Treatment and Prevention Association's model of training patients as community health agents) to promote footwear adoption and hygiene, and to reduce stigma.
Public health interventions: the WHO 2021–2030 NTD roadmap includes podoconiosis as a non-infectious NTD target for national program integration; Ethiopia's Federal Ministry of Health has prioritized podoconiosis elimination given the country's disproportionate global burden. No specific WHO 2030 numeric elimination target for podoconiosis alone was identified in this search (the overarching NTD roadmap targets — 90% reduction in people requiring NTD treatment, 75% reduction in NTD-related DALYs, ≥100 countries eliminating ≥1 NTD — apply at the aggregate NTD-portfolio level).
Environmental interventions: community-level floor covering/soil-contact reduction programs in schools and homes in endemic districts.

14. Other Species / Natural Disease

Podoconiosis, as an environmentally-and-genetically determined human disease dependent on a specific human HLA class II susceptibility architecture and human bipedal barefoot behavior, has no described naturally occurring veterinary or wildlife counterpart in the literature surveyed. No OMIA (Online Mendelian Inheritance in Animals) entry, comparative veterinary case series, or cross-species susceptibility data were identified — this is expected, since livestock/companion animals do not share the same plantar skin exposure pattern, gait, or HLA architecture, and no zoonotic or cross-species transmission mechanism exists (the disease is non-infectious). This is a notable gap relative to many other NTDs but is mechanistically expected given the disease's human-specific gene-environment etiology.

15. Model Organisms

There is no validated whole-animal model that specifically recapitulates podoconiosis as a disease entity (unlike, e.g., filarial lymphedema, which has established animal infection models). However, related experimental and model-organism work is directly relevant to its mechanistic underpinnings:

Historical intralymphatic silica-injection experiments (foundational to the Price-era pathogenesis model; described in the Trans R Soc Trop Med Hyg 1985 silica/lymph-node/vessel study): direct intralymphatic injection of fine silica particles in experimental animals produced an "immediate and intense macrophage reaction with later fibrosis both within lymph vessels and to a lesser extent within lymph nodes," with lymphography showing that the resulting obstruction was driven more by vessel-wall than lymph-node effects — this is the closest thing to a mechanistic animal model of podoconiosis pathogenesis and directly supports the silica/mineral-macrophage-fibrosis causal chain (step 2–7 above). Species and exact citation detail were not fully resolved in this search and should be confirmed against the primary Trans R Soc Trop Med Hyg article before citation as a formal "animal model" record.
General lymphedema models (not podoconiosis-specific, but mechanistically analogous for the downstream lymphatic-obstruction/fibrosis phenotype): the murine tail lymphedema model (surgical ablation of tail lymphatics) and the murine hindlimb secondary lymphedema model (surgical/radiation-based) reproduce the distal-limb swelling and fibrosis phenotype seen in podoconiosis, though they model post-surgical/radiation lymphedema rather than particulate-mineral-induced disease.
Genetic lymphatic-dysfunction model: the Chy mouse (missense VEGFR3/Flt4 mutation) develops congenital chylous ascites and progressive peripheral lymphedema — useful for studying lymphatic vessel biology generally but not etiologically related to podoconiosis's acquired, particulate/immune-mediated mechanism.
Silicosis models (rat intratracheal silica instillation, PMC1008352) are the closest analogous organ-system model for silica-macrophage-fibrosis biology, informing (by analogy to the lung) how crystalline silica engages macrophage phagolysosomal rupture and downstream fibrogenesis in the lymphatic/dermal context of podoconiosis.

Overall assessment: podoconiosis-specific model-organism research is minimal-to-absent in the modern literature; the mechanistic evidence base rests primarily on human tissue/biopsy studies, human genetic-epidemiology (GWAS/family) studies, and historical animal silica-injection experiments from the 1970s–80s, representing a significant translational research gap (no modern in vivo model exists to test candidate interventions before human trials).

Summary of Key Evidence Gaps (for curation awareness)

No modern podoconiosis-specific animal model exists to mechanistically validate the HLA–mineral–macrophage–fibrosis causal chain in vivo.
Epigenetic, proteomic, metabolomic, single-cell, and spatial transcriptomic data are entirely absent from the literature surveyed.
Global burden data outside Ethiopia are sparse; podoconiosis is not yet included in the GBD framework.
The precise antigen/mechanism by which mineral particles engage HLA class II-restricted T-cell activation remains undefined (cytokine-stimulation data are inconsistent/paradoxical, PMC11598685).
No podoconiosis-specific ICD-11/Orphanet code was confirmed in this search and should be verified directly before ontology binding.

Sources

Note on downstream use: All ontology-term suggestions (HPO, GO, CL, UBERON, CHEBI, NCIT) in this report are research leads only, per dismech's anti-hallucination curation policy — each must be independently verified (label match, dynamic-enum reachability) via OAK/just validate-terms before being bound in a KB entry. Several PMIDs above were extracted from search-engine snippets rather than direct PubMed fetches (which were blocked by cookie/CAPTCHA walls during this session); curators should re-verify each PMID against PubMed directly, and re-derive exact-quote snippets from the primary source before use as evidence: blocks, per the dismech-references skill.

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	41
Resolved	41
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	41
On topic	28
Off topic	1

References that may not be about this subject

These identifiers resolve, so they are not fabrications, but the records they resolve to share almost none of this report's vocabulary. That is a clue and not a verdict - a paper can be relevant in ways its title and abstract do not spell out - so read them before deciding:

PMC:PMC1008352 (1 mention) - Intratracheal injection into rats of size-graded silica particles.
shared terms: none

Weighed against this report's own most characteristic terms: podoconiosis, disease, chronic, lymphatic, ethiopia, lymphedema, hla, class, skin, endemic, adla, model, directly, genetic, soil, environmental, secondary, foot, footwear, mechanism.

All extracted references resolved successfully. Resolving is not the same as being relevant, though - see the references listed above as possibly off topic.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome	Count
Terms checked	24
Resolved	24
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	0
Terms whose name was checked	17
Terms named correctly	13
Terms named as a different term	3
Terms whose name is worth a second look	1

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

UBERON:0002387 (2 mentions) - the report calls it "dermis"; UBERON calls it pes
UBERON:0004357 (1 mention) - the report calls it "dorsum of foot"; UBERON calls it paired limb/fin bud
UBERON:0001511 (1 mention) - the report calls it "leg structures"; UBERON calls it skin of leg

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

UBERON:0002391 (1 mention) - the report calls it "lymph node"; UBERON calls it lymph

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Podoconiosis (Endemic Non-Filarial Elephantiasis / Geochemical Lymphedema): Comprehensive Research Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

Causal chain (numbered, with inference status noted)

Detail by mechanism category

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary of Key Evidence Gaps (for curation awareness)

Sources

Reference Validation

References that may not be about this subject

Term Validation

Terms the report names something else

Terms whose name is worth a second look