Bacillary Angiomatosis — Comprehensive Disease Characterization Report

Disease: Bacillary Angiomatosis (BA) MONDO: MONDO:0000758 · Category: Infectious disease (bacterial, vasoproliferative) Report basis: Aggregated disease-level evidence from peer-reviewed literature (reviews, landmark case-control study, mechanistic in vitro/in vivo studies). No individual-patient/EHR dataset was provided; findings are synthesized from PubMed primary literature. Evidence types are flagged as human clinical, in vitro, or model organism.

Summary (Answer to the Research Question)

Bacillary angiomatosis is an angioproliferative (vascular tumor–forming) infectious disease caused by the Gram-negative bacteria Bartonella henselae and Bartonella quintana, occurring almost exclusively in immunocompromised hosts—most classically advanced HIV/AIDS (CD4 typically <100 cells/µL) and also solid-organ transplant recipients—and only rarely in immunocompetent individuals. The bacteria hijack vascular endothelium: the secreted autotransporter BafA acts as a VEGF-receptor-2 agonist, the trimeric autotransporter adhesin BadA activates HIF-1 to drive proangiogenic reprogramming, and the VirB/D4 type IV secretion system injects Bep effectors that inhibit endothelial apoptosis—together producing lobular capillary proliferations in skin and viscera. It is diagnosed by biopsy (Warthin-Starry silver stain, PCR) and is highly curable with prolonged antibiotics (erythromycin or doxycycline), but disseminated untreated disease can be fatal. It is not a genetic disease; there are no causal human genes, and host immunosuppression plus species-specific exposures (cats/cat fleas for B. henselae; homelessness, alcoholism, body lice for B. quintana) are the key determinants.

1. Disease Information

Overview. BA is a rare, treatable, vasoproliferative bacterial infection characterized by tumor-like proliferations of small blood vessels in skin, subcutaneous tissue, and internal organs. First recognized in the HIV/AIDS epidemic of the 1980s, it is caused by chronic infection with Bartonella henselae or B. quintana (formerly genus Rochalimaea) (21285862, 8335458).

Key identifiers. - MONDO: MONDO:0000758 - MeSH: Angiomatosis, Bacillary (D016917) - ICD-10: A44.8 (Other forms of bartonellosis); ICD-11: 1C30.Y (Other specified bartonellosis) - OMIM / Orphanet: Not a Mendelian disease → no OMIM gene entry; not a classic Orphanet rare-genetic entry (infectious etiology) - SNOMED CT: Bacillary angiomatosis (disorder)

Synonyms / alternative names: Bacillary angiomatosis-peliosis (when visceral peliosis coexists); epithelioid angiomatosis; bacillary epithelioid angiomatosis; (historically) Rochalimaea angiomatosis. Bacillary peliosis (hepatis/splenic) is the visceral counterpart.

Information source. Disease-level aggregated resources and primary literature (case series, one landmark molecular case-control study, mechanistic studies), not individual EHR data.

2. Etiology

Causal factors — infectious (not genetic). BA is caused by two Gram-negative bacilli: Bartonella henselae (NCBI:txid38323) and Bartonella quintana (NCBI:txid803). "Bacillary angiomatosis is an infectious disease caused by 2 gram-negative bacilli, Bartonella henselae and Bartonella quintana" (21285862). A permissive host state (immunosuppression) determines progression from infection to vasoproliferation: "The severity of Bartonella infection correlates with the patient's immune status" (24933445).

Risk factors (environmental / host). - Immunosuppression (dominant): advanced HIV/AIDS (e.g., CD4 47 cells/µL, 27428207), solid-organ transplant recipients (22316326). Rare in immunocompetent hosts (21285862, 16495874). - B. henselae exposures: cat contact and cat-flea (Ctenocephalides felis) exposure (P≤0.004) (9407154, 9272384). - B. quintana exposures: low income (P=0.003), homelessness (P=0.004), body-louse exposure (P=0.03) (9407154); chronic alcoholism (7529895). - Genetic risk factors: None known. Not applicable — no susceptibility loci, causal variants, or modifier genes are established for the human host.

Protective factors. Immune competence / immune reconstitution (antiretroviral therapy in HIV) reduces risk and aids cure; ectoparasite control (cat flea control, delousing/hygiene) reduces exposure. No genetic protective variants are described.

Gene–environment interactions. Not applicable in the classical (human-genetic) sense; the operative interaction is host immune status × pathogen exposure (e.g., cat/flea or louse contact in an immunosuppressed host).

3. Phenotypes (with suggested HPO terms and qualitative frequencies)

BA phenotypes are clinical signs/physical manifestations (cutaneous vascular lesions), symptoms (fever, malaise), and laboratory abnormalities (anemia, thrombocytopenia). Onset is adult (tracks the immunosuppressed adult population); severity ranges mild-to-severe; course is progressive if untreated, resolving with therapy.

Quality-of-life impact: Painful/disfiguring skin lesions, bleeding, and systemic constitutional symptoms impair function; visceral disease can be life-threatening. No formal EQ-5D/SF-36 data exist for BA specifically; QoL burden is inferred from lesion morbidity and treatable nature.

4. Genetic / Molecular Information

Not applicable to the human host — BA is a bacterial infection, not an inherited disorder. There are no causal human genes, pathogenic germline/somatic variants, ClinVar entries, allele frequencies, modifier genes, epigenetic disease signatures, or chromosomal abnormalities.

The relevant "molecular" players are bacterial virulence genes (host-microbe interaction): - bafA — proangiogenic autotransporter; passenger domain functions as a VEGF analog (32678094); homologs in B. quintana, B. bacilliformis, B. elizabethae (35379004, 36810719). - badA (Bartonella adhesin A) — trimeric autotransporter adhesin; head domain mediates host adhesion and HIF-1 activation (18627378, 21557057). - virB/virD4 T4SS and Bep effector genes — translocation of effectors inhibiting apoptosis and driving proangiogenic phenotype (23163798). - B. quintana Vomps (variably expressed outer-membrane proteins) and Trw conjugation system for erythrocyte adherence (21557057).

5. Environmental Information

• Infectious agents (causal): Bartonella henselae and Bartonella quintana (Alphaproteobacteria; family Bartonellaceae). B. henselae also causes cat scratch disease and peliosis hepatis; B. quintana also causes trench fever and endocarditis (18444576, 24933445). A rare BA case from B. elizabethae has been reported (36810719).
• Vectors/reservoirs: B. henselae — reservoir cats, vector cat flea Ctenocephalides felis; B. quintana — reservoir humans, vector body louse Pediculus humanus corporis (9272384).
• Lifestyle factors: homelessness, poverty, chronic alcoholism (for B. quintana); cat ownership/exposure (for B. henselae) (9407154, 7529895).
• Toxins/radiation/occupational exposures: Not applicable.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating infection → clinical lesion)

1. Exposure/inoculation — a cat scratch/flea (B. henselae) or body louse (B. quintana) introduces Bartonella into skin/blood of a (usually immunocompromised) host. (human clinical/epidemiologic; 9407154)
2. Bacterial adhesion — the trimeric autotransporter adhesin BadA binds fibronectin/ECM and endothelial cells, leading to autoagglutination and firm attachment. (in vitro; 18627378, 21557057)
3. Proangiogenic reprogramming (branch A) — BadA engagement activates HIF-1, which results in transcription of angiogenic genes and autocrine VEGF secretion by endothelial cells. (in vitro; 18627378, 23163798)
4. VEGFR-2 mitogenic signaling (branch B) — the secreted autotransporter BafA binds VEGF receptor-2 and activates its downstream pathway (functioning as a VEGF analog), driving endothelial proliferation, tube formation, and microvessel sprouting. (in vitro + mouse; 32678094)
5. Anti-apoptotic survival (branch C) — the VirB/D4 T4SS translocates Bep effectors into endothelial cytoplasm, causing invasome-mediated uptake of bacterial aggregates and inhibiting apoptosis, so proliferating endothelium survives. (in vitro; 23163798)
6. Stromal amplification — infected pericytes increase VEGF with reduced coverage (23184416), and persistence in mesenchymal stromal cells further amplifies endothelial activation/angiogenesis (34031126). (in vitro)
7. Lesion formation — combined proliferation + survival + inflammation produces a lobular capillary proliferation lined by plump epithelioid endothelial cells with neutrophilic infiltrate and stromal bacterial aggregates — the histologic bacillary angioma. (human clinical; 24718378)
8. Dissemination — because host immunity is impaired, lesions spread hematogenously to viscera (liver/spleen peliosis, bone, GI tract, CNS), which can lead to organ dysfunction, hemorrhage, and death if untreated. (human clinical; 11362939, 24933445)

Upstream vs downstream: Adhesion (BadA) and effector delivery (VirB/D4) are upstream; VEGF/VEGFR-2 signaling, HIF-1 activation, and apoptosis inhibition are the core intermediate nodes; endothelial proliferation → lesion formation → dissemination are downstream.

Molecular pathways: VEGF/VEGFR-2 signaling, HIF-1α transcriptional program, NF-κB–associated proangiogenic/anti-apoptotic signaling. KEGG/Reactome: VEGF signaling pathway; HIF-1 signaling pathway. Cellular processes: angiogenesis, endothelial proliferation, inhibition of apoptosis, inflammation. Immune involvement: disease is permitted by immunodeficiency; lesions show mixed neutrophilic/lymphocytic infiltrate; in immunocompetent hosts a granulomatous response contains infection (9784568). Suggested GO terms: angiogenesis (GO:0001525); sprouting angiogenesis (GO:0002040); VEGF receptor signaling pathway (GO:0048010); cellular response to hypoxia (GO:0071456); negative regulation of apoptotic process (GO:0043066); inflammatory response (GO:0006954). Suggested CL terms: endothelial cell (CL:0000115); blood vessel endothelial cell (CL:0000071); pericyte (CL:0000669); mesenchymal stem cell (CL:0000134); erythrocyte (CL:0000232, for B. quintana bacteremia). Omics: No human disease transcriptomic/proteomic/metabolomic BA signatures are established; mechanistic data are protein/pathway-level (VEGF, HIF-1, BafA/BadA/Bep).

7. Anatomical Structures Affected

• Primary organ: skin (UBERON:0002097) and subcutaneous tissue (UBERON:0002072) — cutaneous/subcutaneous vascular nodules.
• Secondary/visceral organs: liver (UBERON:0002107; peliosis hepatis), spleen (UBERON:0002106), bone/bone marrow (UBERON:0002481/UBERON:0002371; lytic lesions, long bones), lymph nodes (UBERON:0000029), GI tract (UBERON:0000160; esophagus/stomach/duodenum), oral mucosa (UBERON:0003343), lung (UBERON:0002048), heart/pericardium, CNS/brain (UBERON:0000955) (11362939, 12894361, 16495874).
• Body systems: primarily cardiovascular/vascular (endothelium), with integumentary, hepatobiliary, skeletal, lymphatic/hematologic, digestive, and occasionally nervous involvement.
• Tissue/cell level: vascular (connective/endothelial) tissue; target cells = vascular endothelial cells (CL:0000115), with pericytes (CL:0000669) and stromal cells; B. quintana/B. henselae also infect erythrocytes (CL:0000232) causing bacteremia.
• Subcellular: bacteria localize extracellularly (stromal aggregates) and are taken up intracellularly via the invasome; effectors act in the endothelial cytoplasm/plasma membrane (GO:0005886 plasma membrane; GO:0005829 cytosol).
• Lateralization: typically multifocal/bilateral and disseminated rather than lateralized; cutaneous lesions are widely distributed.

8. Temporal Development

• Onset: adult-onset (parallels immunosuppressed adults); subacute/chronic/insidious course over weeks to months (e.g., 6-month growing lesions, 23282705; 10-month nodule, 9205511).
• Progression: progressive if untreated, from localized papules to disseminated visceral disease; can be rapidly life-threatening with hemorrhage/organ involvement (12894361, 18098054).
• Course pattern: treatment-induced remission is the rule with adequate therapy; relapse occurs with inadequate/short courses (9272384, 9205511).
• Duration: not self-limited in immunocompromised hosts (requires antibiotics); may resolve with prolonged therapy and immune reconstitution.
• Critical intervention window: early biopsy-based diagnosis and prompt antibiotics prevent dissemination and death; immune restoration (ART) is a key adjunct.

9. Inheritance and Population

• Epidemiology: Rare; no precise population prevalence/incidence figures exist (opportunistic, under-reported). Incidence fell sharply in high-income settings after combination antiretroviral therapy reduced severe HIV immunosuppression; it remains under-recognized in sub-Saharan Africa despite high HIV prevalence (24718378). B. quintana seroprevalence is high in homeless populations (IgG ≥1:128 in 57% and ≥1:1024 in 11% of Tokyo homeless; 16495631); B. quintana bacteremia in 14% of Marseille homeless (9895398).
• Inheritance: Not applicable (infectious disease; no Mendelian inheritance, penetrance, expressivity, anticipation, mosaicism, founder effect, consanguinity, or carrier frequency).
• Demographics: predominantly adults with immunosuppression; historically HIV-infected men; B. quintana clusters in homeless/alcoholic, low-income urban populations. No strong ethnic predisposition beyond socioeconomic exposure patterns. Sex ratio reflects the underlying at-risk populations rather than intrinsic disease bias.
• Geographic distribution: worldwide; B. quintana ("urban trench fever") in homeless populations across the US, Europe, and Japan (11871479, 16495631).

10. Diagnostics

• Biopsy/histopathology (gold standard): lobular proliferation of capillaries lined by plump, epithelioid/spindled endothelial cells; mixed neutrophilic/leukocytoclastic infiltrate; extracellular amphophilic granular material (bacterial aggregates) (24718378, 12152480). Warthin-Starry silver stain highlights clumps of bacilli — "A Warthin-Starry stain highlighted clumps of bacilli, confirming the diagnosis of BA" (24718378). Electron microscopy can visualize bacilli (11362939).
• Molecular: PCR of lesional tissue (e.g., 16S rRNA, citrate synthase gltA, riboflavin synthase ribC, or a 298-bp Bartonella fragment) identifies and speciates the organism and can monitor treatment response (9205511, 7529895, 40090362).
• Serology: indirect immunofluorescence antibody (IFA) for Bartonella-specific IgG/IgM; useful epidemiologically but poorly reliable for individual BA diagnosis (9272384, 11362939).
• Culture: possible but difficult/fastidious, slow-growing; low sensitivity (9272384).
• Imaging: CT/MRI/ultrasound to define visceral (hepatosplenic peliosis, abscesses) and osseous lesions (27428207, 22316326).
• Laboratory: anemia, thrombocytopenia, elevated inflammatory markers may accompany systemic disease.
• Genetic/omics testing: Not applicable (no human genetic test; no karyotype/CMA/mtDNA/repeat-expansion role).
• Differential diagnosis: Kaposi sarcoma (key mimic), pyogenic granuloma, angiosarcoma, epithelioid hemangioma, verruga peruana (B. bacilliformis), cat-scratch disease — distinguished by Warthin-Starry-positive bacilli and vascular-proliferative histology (10718405, 31780437). BA is antibiotic-curable, unlike KS.
• Screening: No population screening; consider B. quintana testing in symptomatic homeless/alcoholic patients and BA in HIV patients with vascular skin lesions.

11. Outcome / Prognosis

• Survival/mortality: With appropriate prolonged antibiotics, prognosis is excellent (lesions resolve). Untreated Bartonella infection can cause high mortality (24933445); disseminated/visceral disease (e.g., GI hemorrhage, panserositis) is potentially fatal (12894361, 18098054).
• Morbidity: disfiguring/painful, friable, bleeding skin lesions; visceral organ dysfunction; bone pain/lytic lesions. No standardized disability/QoL metrics for BA.
• Disease course/complications: hemorrhage from friable lesions, airway/oronasal involvement (oronasal fistula, 28902296), massive GI bleeding (12894361), anemia and multi-serosal involvement (18098054).
• Recovery potential: high with treatment + immune reconstitution; relapse if therapy is too short.
• Prognostic factors: degree/duration of immunosuppression (CD4 count), extent of dissemination, timeliness of diagnosis and adequacy/duration of antibiotics. PCR negativity of lesional material is a favorable treatment-response marker (9205511).

12. Treatment

• First-line pharmacotherapy: Erythromycin (macrolide) is first-line for angioproliferative lesions — "erythromycin is the first-line antibiotic therapy for the treatment of angioproliferative lesions" (24933445). Doxycycline (tetracycline) is the principal alternative — "Doxycycline led to complete resolution" (28902296). Azithromycin and clarithromycin are also effective (21285862, 18098054).
• Duration: prolonged — erythromycin for at least three months is recommended (or doxycycline) to prevent relapse in immunocompromised patients (11362939).
• Severe/systemic disease: add rifampicin; gentamicin + doxycycline for associated bacteremia/endocarditis (24933445).
• Adjuncts: antiretroviral therapy for immune reconstitution in HIV patients (27428207); treat/eliminate ectoparasites.
• Surgical/interventional: localized excision has been used but relapse/dissemination risk means antibiotics are essential (12152480, 16495874).
• Advanced/experimental therapeutics (gene/cell/RNA/targeted/immunotherapy): Not applicable — antibiotics are curative; no such therapies are used.
• Adverse events: relate to the antibiotics used (GI intolerance with erythromycin/doxycycline; photosensitivity with doxycycline); a Jarisch-Herxheimer-like reaction can occur at treatment initiation.
• Suggested NCIT/CHEBI terms: Erythromycin (NCIT:C578; CHEBI:42355); Doxycycline (NCIT:C513; CHEBI:50845); Azithromycin (NCIT:C609; CHEBI:2955); Clarithromycin (CHEBI:3732); Rifampicin (NCIT:C29408; CHEBI:28077); Gentamicin (NCIT:C61796; CHEBI:27412).

13. Prevention

• Primary prevention: avoid the exposures — for B. henselae: cat-flea control, prompt cleaning of cat scratches, caution around cats (esp. for immunosuppressed) (22316326); for B. quintana: body-louse control/delousing, hygiene, and addressing homelessness (9895398, 11871479).
• Secondary prevention: early recognition and biopsy of vascular skin lesions in immunosuppressed/homeless patients; prompt antibiotics prevent dissemination.
• Tertiary prevention: adequate-duration antibiotics + immune reconstitution (ART) to prevent relapse and complications.
• Immunization: None available (no vaccine).
• Public-health interventions: vector control (fleas/lice), sanitation and services for homeless populations, clinician awareness.
• Genetic counseling/screening: Not applicable (non-genetic).
• Prophylaxis: no established antibiotic prophylaxis; risk-factor reduction is the mainstay.

14. Other Species / Natural Disease

• Taxonomy of pathogens: Bartonella henselae (NCBI:txid38323), Bartonella quintana (NCBI:txid803); related agents of pathological angiogenesis include B. bacilliformis (verruga peruana; NCBI:txid774) and B. elizabethae (NCBI:txid34113) (35379004, 36810719).
• Natural reservoir/animal disease: Cats (Felis catus, NCBI:txid9685) are the natural reservoir of B. henselae, harboring asymptomatic intraerythrocytic bacteremia — they are typically infected but not diseased (do not develop BA) (18444576, 21637717). Fleas (Ctenocephalides felis) and, for B. quintana, human body lice are vectors/reservoirs (35545848, 40090362).
• Comparative biology: B. henselae induces angiogenesis in human endothelial cells but not feline endothelial cells, highlighting host-specific susceptibility (21637717). Bartonella is the only bacterial genus known to induce pathological angiogenesis in mammals (23184416).
• Zoonotic potential: B. henselae is a zoonosis (cat-to-human via scratch/flea); B. quintana is human-adapted (louse-borne, human reservoir) (9272384). No orthologous human "disease gene" applies (bacterial etiology).
• VBO breed associations: Not applicable.

15. Model Organisms

• In vitro (primary models): human umbilical vein and skin microvascular endothelial cell lines (accelerated angiogenesis/wound healing on B. henselae infection; 21637717); human brain vascular pericytes (increased VEGF; 23184416); mesenchymal stromal cells (persistence amplifying angiogenesis; 34031126); recombinant BafA passenger domain assays (EC proliferation, tube formation, sprouting; 32678094).
• Mouse model: immunocompetent C57BL/6 mice given intraperitoneal B. henselae develop granulomatous hepatitis peaking week 4, resolving by 12 weeks, with hepatic bacterial DNA persistence ≥3 months (9784568). (model organism)
• In vivo angiogenesis: BafA drives angiogenesis in mice (32678094).
• Genetic/transgenic disease models: Not applicable — BA is an infection; there are no knockout/knock-in "BA models." Bacterial mutants (e.g., badA⁻, bafA transposon mutants, virB/D4 strains) are used to dissect virulence (18627378, 32678094, 23163798).
• Phenotype recapitulation & limitations: cellular models reproduce the angiogenic/anti-apoptotic signaling; the mouse model reproduces granulomatous containment in an immunocompetent host but not the disseminated vasoproliferative tumors of immunocompromised humans — underscoring that human immunosuppression is essential to full disease.

Supported and Refuted Hypotheses

Supported: 1. BA is caused by B. henselae and B. quintana and occurs mainly in immunosuppressed hosts. (21285862 24933445) 2. Vasoproliferation is driven by bacterial proangiogenic factors: BafA (VEGFR-2 agonist), BadA (HIF-1 activation), and VirB/D4-delivered Beps (apoptosis inhibition). (32678094 18627378 23163798) 3. The two species have partly distinct tropism/exposures: B. quintana → subcutaneous/lytic bone lesions, homeless/louse-associated; B. henselae → peliosis hepatis, cat/flea-associated. (9407154) 4. Diagnosis rests on Warthin-Starry histopathology + PCR; treatment with prolonged macrolide/tetracycline is curative. (24718378 11362939 24933445)

Refuted / excluded: - BA is not a genetic/heritable disease; no human causal genes, variants, or inheritance pattern apply. - BA is not a neoplasm despite tumor-like appearance; it is a reversible, antibiotic-curable infection (distinguishing it from its mimic Kaposi sarcoma).

Limitations and Future Directions

• Epidemiology lacks precise prevalence/incidence rates (rare, opportunistic, under-reported); QoL and formal outcome metrics are absent for BA specifically.
• Mechanistic data derive largely from in vitro human EC/pericyte systems and B. henselae; fewer B. quintana mechanistic studies exist, and no immunocompromised animal model fully reproduces disseminated human BA.
• Future work: an immunodeficient animal model of disseminated BA; comparative B. quintana vs B. henselae proangiogenic effector biology; molecular epidemiology in under-studied high-HIV-burden regions.

Evidence base: ~15 primary references (reviews, one landmark NEJM molecular case-control study [PMID 9407154], mechanistic in vitro/in vivo studies). Evidence types span human clinical (case series/epidemiology), in vitro (endothelial/pericyte/effector studies), and model organism (mouse). No individual-patient dataset was provided.