Primary Amebic Meningoencephalitis (PAM) — Comprehensive Disease Profile

MONDO: MONDO:0000290 · Category: Infectious disease · Causal agent: Naegleria fowleri (free-living thermophilic amoeba; NCBI Taxon:5763)

Causal "gene" note. PAM is not a human genetic disease and has no human causal gene. The template's "Causal gene(s): not recorded" field is correct and expected: the disease is produced by infection with the free-living amoeba Naegleria fowleri. Where this report refers to "causal genes," these are pathogen (amoeba) virulence genes (e.g., nfa1, naegleriapore/Npa, cathepsin/serine-protease genes), not host germline genes. All subsequent sections should be read with the pathogen as the etiologic agent.

1. Disease Information

Overview. Primary amebic meningoencephalitis (PAM) is a rapidly progressive, fulminant, almost universally fatal infection of the central nervous system caused by the thermophilic, free-living amoeba Naegleria fowleri ("brain-eating amoeba"). Infection occurs when warm fresh water containing the amoeba is forced into the nose; the organism crosses the cribriform plate along the olfactory nerve and invades the brain, producing a hemorrhagic, necrotizing meningoencephalitis (22919000). Death typically occurs within ~1–2 weeks of symptom onset, with a case-fatality rate >95–97% (39432113).

Key identifiers. - Mondo: MONDO:0000290 - ICD-10: B60.2 (Naegleriasis / primary amebic meningoencephalitis) - ICD-11: 1F55 (Acanthamoebiasis / free-living amoeba infections) → Naegleria meningoencephalitis - MeSH: D008836 Meningoencephalitis; organism MeSH D009258 Naegleria; D054314 Central Nervous System Protozoal Infections - SNOMED CT: 36649002 (Primary amebic meningoencephalitis) - Orphanet: Not a classic rare-genetic ORPHA entry; covered under free-living amoebic infections - OMIM: Not applicable (no Mendelian locus) - NCBI Taxonomy (agent): Naegleria fowleri Taxon:5763

Synonyms / alternative names. Naegleriasis; Naegleria fowleri infection; "brain-eating amoeba" infection; amebic meningoencephalitis (primary); PAM; PAME.

Information source type. Disease-level, aggregated from case reports, CDC Free-Living Ameba (FLA) surveillance, and systematic reviews (32369575 26582886). Because PAM is extremely rare, there are no large EHR cohorts; evidence is predominantly individual case/autopsy data pooled at the disease level.

2. Etiology

Primary cause (infectious). The sole cause is infection with Naegleria fowleri, a thermophilic free-living amoeba found worldwide in warm fresh water (lakes, ponds, rivers, hot springs, geothermal water) and in inadequately disinfected recreational/treated water (pools, splash pads, tap water) (40146665 22919000 27123690). The amoeba has three life stages: trophozoite (invasive, feeding), flagellate (transient), and cyst (environmentally resistant). Only the trophozoite invades tissue.

Route of entry. Intranasal instillation of contaminated water (swimming, diving, splashing, hot-spring bathing, religious ablution/wudu, and nasal/sinus irrigation with neti pots using contaminated tap water) (22919000 21291600). In Karachi, Pakistan, a cluster of 13 PAM cases occurred in people with no aquatic exposure, with infection attributed to ablution with tap water; N. fowleri was subsequently detected in Karachi municipal tap water (11/39 samples) under conditions of high temperature, low chlorine, and high coliform counts (21291600 39780139).

Risk factors (environmental/behavioral). - Warm-freshwater nasal exposure — strongest risk; swimming/diving is the most common exposure and lakes/ponds/reservoirs the most common source (32369575). - Male sex (~75–76% of cases) (32369575 26582886). - Young age (children/adolescents; median 12–14 years) (32369575 26582886). - Warm climate / summer months / southern latitudes, with geographic expansion northward attributed to climate warming (22919000 26582886). - Inadequately disinfected treated water (splash pads, pools, household plumbing) (40146665 22919000). - Nasal irrigation with non-sterile tap water (22919000).

Genetic risk/protective factors (host). None established — PAM is not a heritable disorder and no human susceptibility/protective loci are validated. (Not applicable.)

Protective factors (environmental). Keeping water out of the nose; using nose clips; using sterile/distilled/boiled water for nasal irrigation; adequate water chlorination (free chlorine ≥1 ppm) — all reduce risk (CDC guidance; 40146665).

Gene–environment interactions (host). Not applicable (no human genetic component). The relevant interaction is pathogen virulence gene expression × host nasal exposure/temperature: thermophilic growth (optimal ~42–45 °C) and virulence-gene upregulation on contact with host cells drive invasion (40096149 33843581).

3. Phenotypes

PAM is clinically biphasic, progressing from nonspecific flu-like illness to fulminant meningoencephalitis (26582886). Onset is acute, typically 1–9 days (median ~5 days) after exposure; course is rapidly progressive, death in a median of ~5 days from symptom onset.

Frequencies from Indian systematic review (fever 79.2%, headache 58.3%, seizures 41.6%; 42764041) and Kerala series (fever 91.7%, headache 83.3%, altered mental status 50%; 41873284).

Laboratory-abnormality phenotypes (CSF). Resembles bacterial meningitis: elevated opening pressure, neutrophilic pleocytosis (median 2400 cells/µL), low glucose (median 23 mg/dL), high protein (median 365 mg/dL); motile trophozoites on wet mount are diagnostic (26582886). HPO: HP:0002922 Increased CSF protein; HP:0003112 (abnormal CSF); low CSF glucose.

Severity / progression. Uniformly severe and progressive; essentially no stable or episodic course. Quality-of-life impact: for the few survivors, outcomes range from full recovery to severe neurological sequelae (cognitive, motor deficits); for the vast majority the outcome is death, so QoL instruments (EQ-5D/SF-36) are not meaningfully applied at the population level.

4. Genetic / Molecular Information

Human causal genes: None (not a genetic disease).

Pathogen (amoeba) "virulence genes" (the functional equivalent of causal molecular drivers): - nfa1 — encodes a ~13.1 kDa pseudopod/food-cup protein central to contact-dependent cytolysis; a validated virulence/vaccine antigen (22955499). - Naegleriapores / Npa (A and B) — pore-forming, membrane-permeabilizing polypeptides causing host-cell lysis (39432113). - Cathepsin B and serine/cysteine proteases — degrade host extracellular matrix and tissue; secreted and packaged in extracellular vesicles (39432113 40312759). - Leishmanolysin (GP63-like metalloprotease) — adhesion/enzymatic virulence, identified in EV proteome (40312759). - Mp2CL5 membrane protein; lysozyme, cystatin, hemerythrin (host-defense evasion, brain migration, lethal infection) (40096149). - Lectins mediating adhesion (32716210).

Genome. N. fowleri genome sequenced; comparative genomics distinguishes pathogenic N. fowleri from non-pathogenic N. gruberi, though several "virulence" homologs are shared, implying regulation/expression (not mere presence) determines pathogenicity (33843581 31797948).

Variant classification / allele frequency / somatic-vs-germline / modifier genes / epigenetics / chromosomal abnormalities (human): Not applicable — there are no human pathogenic variants, ClinVar entries, gnomAD frequencies, or chromosomal findings for this infectious disease.

5. Environmental Information

• Environmental reservoir: warm fresh water worldwide — lakes, ponds, rivers, hot springs, geothermal discharge, poorly maintained pools/splash pads, and warm tap/plumbing water (40146665 22919000). Thermophilic: thrives up to ~45 °C.
• Climate sensitivity: warming water temperatures expand the amoeba's range; northward spread of US cases documented (22919000 26582886).
• Lifestyle/behavioral factors: recreational freshwater activities (swimming, diving, water-skiing, splash pads), hot-spring bathing, and nasal/sinus irrigation with untreated tap water (22919000).
• Infectious agent (NCBI Taxonomy): Naegleria fowleri (Taxon:5763), phylum Percolozoa, class Heterolobosea. Related non-pathogenic congener: N. gruberi. Other pathogenic FLA causing distinct CNS disease: Acanthamoeba spp., Balamuthia mandrillaris (granulomatous amebic encephalitis), Sappinia (33843581).

6. Mechanism / Pathophysiology

Ordered causal chain (initiating exposure → clinical manifestation):

1. Contaminated warm freshwater is forced into the nasal cavity (swimming, diving, hot-spring bathing, or nasal irrigation) → deposits N. fowleri trophozoites on the olfactory/nasal mucosa (demonstrated, 22919000).
2. Trophozoites adhere to nasal mucosa via lectins/food-cup (Nfa1) structures and begin feeding on epithelium → local mucosal damage (demonstrated in vitro/animal, 32716210 22955499).
3. Amoebae migrate along olfactory nerve fibers through the cribriform plate into the olfactory bulbs (demonstrated; explains early anosmia, 22919000).
4. In the CNS, trophozoites perform contact-dependent trogocytosis/phagocytosis ("food-cup" ingestion of neural cells), driven by actin dynamics regulated by Arp2/3 and Src kinase (demonstrated, 40096149).
5. Simultaneously, contact-independent cytolysis occurs via secreted and extracellular-vesicle–delivered virulence factors — naegleriapores (pore formation), cathepsin B/serine proteases, phospholipases, leishmanolysin — causing hemolysis, increased membrane permeability, and necrosis (demonstrated in vitro, 40312759 39432113).
6. Tissue destruction + amoebic antigens trigger a massive innate inflammatory response (neutrophil and eosinophil influx, cytokine release) → necrotizing, hemorrhagic meningoencephalitis with cerebral edema (demonstrated; neutrophils central to host defense, 2628288 27525348).
7. Cerebral edema and inflammation → raised intracranial pressure, uncal/tonsillar herniation → brainstem compression (inferred from clinical/autopsy data, 25667249).
8. → Coma and death, typically within days (demonstrated clinical outcome, 26582886).

Branch: Beyond primary olfactory-bulb invasion, autopsy and animal data indicate extra-CNS hematogenous dissemination can occur (relevant to transplant-transmission risk) (24279908).

Molecular pathways / cellular processes. - Host-cell ingestion: actin cytoskeleton remodeling (Arp2/3, Src kinase) — GO:0030041 actin filament polymerization; GO:0006909 phagocytosis; "trogocytosis" (40096149). - Cytolysis: pore-forming/membrane permeabilization (naegleriapores) — GO:0051715 cytolysis in another organism; GO:0006887 EV/exocytosis. - Proteolysis: cysteine/serine protease activity — GO:0006508 proteolysis (39432113). - Metabolic shift: brain-passaged amoebae show altered lipid storage/utilization vs axenic culture (Raman microspectroscopy) (40096149). - Immune involvement: innate-dominant neutrophilic/eosinophilic inflammation; adaptive immunity can be protective in animal models (2628288 646016).

Tissue-damage mechanisms: necrosis, hemorrhage, phagocytic "nibbling" of neurons, protease-mediated matrix degradation, oxidative inflammatory injury.

Molecular profiling (transcriptomics/proteomics). RNA-seq across life stages shows stage-specific regulation of the cytoskeletal machinery: nf-profilin (actin-binding regulator) is high in cysts and membrane-localized, whereas nf-actin localizes to cytoplasm, pseudopodia, and food-cup structures of trophozoites; during cyst→trophozoite conversion on host-cell contact, profilin falls and actin rises — directly linking the transcriptome to the invasive food-cup apparatus (40016342 36839446). Secretome/EV proteomics identified >1000 proteins including leishmanolysin and serine proteases (40312759). Brain-passaged vs axenic amoebae differ metabolically in lipid storage/utilization (Raman spectroscopy) (40096149). Transcriptomic profiling of the "brain-eating amoeba" host interaction further catalogs virulence-associated expression (39735262). Phylogenomics places N. fowleri in phylum Heterolobosea, new order Naegleriida (39826589).

Suggested ontology terms: GO:0006909 (phagocytosis), GO:0030041 (actin polymerization), GO:0006508 (proteolysis), GO:0019835 (cytolysis), GO:0006954 (inflammatory response); CL:0000540 neuron, CL:0000127 astrocyte, CL:0000775 neutrophil; UBERON:0002264 olfactory bulb, UBERON:0000955 brain.

7. Anatomical Structures Affected

• Primary organ: Brain (UBERON:0000955), especially olfactory bulbs (UBERON:0002264), frontal lobes, and basal cisterns; meninges (UBERON:0002360). Nervous system (central).
• Portal of entry tissue: nasal/olfactory epithelium (UBERON:0001707 nasal cavity; UBERON:0001997 olfactory epithelium) and cribriform plate / olfactory nerve (UBERON:0001675).
• Secondary / disseminated involvement: rare extra-CNS spread (lung, heart, kidney reported at autopsy), relevant to transplant risk (24279908).
• Tissue/cell level: nervous tissue — neurons (CL:0000540), astrocytes/glia (CL:0000125); inflammatory infiltrate of neutrophils (CL:0000775) and eosinophils (CL:0000771).
• Subcellular (host damage): plasma-membrane disruption (pore-forming peptides); for the amoeba, food cup / pseudopod (amoebic phagocytic structure), lysosomes/EVs (GO:0005764 lysosome; GO:1903561 extracellular vesicle).
• Lateralization: typically bilateral but may begin asymmetric reflecting unilateral olfactory-tract seeding; progresses to diffuse cerebral involvement.

8. Temporal Development

• Onset: Acute. Incubation ~1–9 days (median ~5) after nasal exposure (26582886).
• Stages: (i) Early — nonspecific flu-like: fever, headache, nausea/vomiting, altered smell/taste; (ii) Late — CNS: meningismus, confusion, seizures, focal deficits, coma (26582886).
• Progression rate: Rapid/fulminant. Median time from symptom onset to death ~5 days; most die within 1–2 weeks (32369575 26582886).
• Course pattern: monophasic, progressive; no relapsing–remitting or episodic form.
• Duration/remission: self-limited only in the sense of rapid death; treatment-induced survival is rare and depends on very early recognition (25667249).
• Critical window for intervention: the first 24–72 hours after symptom onset — survival correlates with early diagnosis and immediate combination therapy (27525348 25667249).

9. Inheritance and Population

• Inheritance: Not applicable (infectious; no germline transmission, penetrance, anticipation, founder effects, or carrier frequency).
• Incidence/prevalence: Extremely rare. ~0–8 US cases/year (CDC); ~381 global cases reported through 2018 (32369575); ~142 US cases 1937–2013 (26582886). True incidence likely underestimated due to misdiagnosis.
• Case-fatality rate: >95–97%; only ~7 confirmed survivors globally in the 2018 review (32369575 39432113).
• Sex ratio: male-predominant ~3:1 (75–76% male) (32369575 26582886).
• Age distribution: predominantly children and adolescents, median 12–14 years, though cases span 13 days to 85 years (42764041).
• Geographic distribution: worldwide in warm climates; US cases concentrated in southern-tier states (Texas, Florida — Florida accounts for >25% of US cases) with northward expansion (Minnesota, Kansas, Indiana) linked to warming (23621053 22919000). Substantial case loads reported from Pakistan, India, Australia, and other warm regions (42764041 41873284). Pakistan (Karachi) is notable for a non-recreational, ablution/tap-water–associated disease pattern (13-case cluster; N. fowleri confirmed in municipal tap water), reflecting high ambient temperature, under-chlorination, and degraded distribution systems (21291600 39780139).

10. Diagnostics

• CSF analysis: bacterial-meningitis-like profile — neutrophilic pleocytosis, low glucose, high protein, raised opening pressure (26582886).
• Direct microscopy (first-line, rapid): wet-mount of fresh CSF showing motile trophozoites — positive in 95.8% of Indian cases; Giemsa/Wright/trichrome staining (do NOT rely on Gram stain) (42764041 23710088).
• Molecular confirmation: real-time PCR of CSF/tissue (CDC) — definitive; LAMP assays for rapid water/clinical detection (35020127 25822175). PCR confirmation is underused in resource-limited settings (only 2/24 Indian cases) (42764041).
• Culture: CSF on non-nutrient agar with E. coli overlay; flagellation test (trophozoite→flagellate in distilled water) (35020127).
• Immunologic: immunohistochemistry/indirect immunofluorescence on tissue; antigen detection.
• Imaging: CT/MRI shows nonspecific cerebral edema, basal meningeal enhancement, hemorrhage; often normal early (26582886).
• Clinical criteria / differential diagnosis: PAM should be suspected in acute meningoencephalitis with recent freshwater nasal exposure (40146665). Differential: bacterial meningitis, viral/herpes encephalitis, fungal meningitis, tuberculous meningitis — distinguished by motile amoebae on wet mount and PCR, and by negative bacterial/viral cultures (27123690).
• Screening: No asymptomatic screening exists (too rare, too rapid); environmental water testing (PCR/LAMP) supports outbreak investigation (25822175).
• Suggested LOINC concepts: CSF cell count/differential, CSF glucose, CSF protein, Naegleria PCR.

11. Outcome / Prognosis

• Mortality: >95–97%; historically near-uniformly fatal (32369575 39432113).
• Survival: only a handful of confirmed survivors worldwide; 3 well-documented North American survivors by mid-2010s (25667249 27525348).
• Prognostic factors: time to diagnosis and treatment is the dominant determinant; early presentation (flu-like stage), prompt combination antimicrobials, aggressive ICP control, and therapeutic hypothermia are associated with survival (25667249 27525348).
• Morbidity in survivors: variable — from near-complete recovery to permanent neurological deficits (cognitive, motor, visual).
• Complications: cerebral edema, herniation, raised ICP, seizures, status epilepticus, hydrocephalus (25667249).
• Disease-specific mortality: essentially all deaths attributable directly to CNS infection within days–weeks.

12. Treatment

No single proven cure; management is a multidrug + neurocritical-care bundle started emergently on suspicion.

• Amphotericin B (polyene antifungal; amebicidal) — backbone, given IV and intrathecal/intraventricular; mainstay in nearly all regimens (used in 91.6% of Indian cases) (42764041 23710088). NCIT: Amphotericin B (C280).
• Miltefosine (alkylphosphocholine; investigational, CDC-provided) — added to regimens of recent survivors (26679626 25667249). NCIT: Miltefosine (C61769).
• Adjunct antimicrobials: azithromycin, fluconazole (or other azoles), rifampin — commonly combined (27525348).
• Neurocritical care: aggressive management of elevated intracranial pressure using traumatic-brain-injury principles, CSF diversion (intraventricular shunt), and therapeutic (targeted) hypothermia — credited in survivors (25667249 27525348). NCIT: Therapeutic Hypothermia.
• Supportive care: mechanical ventilation, seizure control, dexamethasone for edema.
• Treatment outcomes: despite therapy, most cases are fatal; survival clusters around early-treated, miltefosine-containing, hypothermia-managed cases (26679626).
• Experimental / preclinical pipeline: A high-throughput phenotypic screen of 12,000 ReFRAME compounds found 58 potent inhibitors (IC50 <1 µM) of free-living amoebae, including 19 active against N. fowleri; 19 compounds killed N. fowleri in vitro within 24 h — faster than current drugs — including HDAC inhibitors (quisinostat, panobinostat, pracinostat, dacinostat, fimepinostat), HSP90 inhibitors (radicicol, NVP-HSP990), halofuginone, fumagillin, bardoxolone, solithromycin, and acriflavine (32970675). Natural products (e.g., Pinus densiflora leaf extract, IC50 62.3 µg/mL) are selectively amebicidal while sparing rat glial cells (38835258). None are yet approved for human PAM.
• Personalized/experimental: no approved targeted therapy. Pharmacogenomics not applicable (pathogen, not host-genome driven).

Suggested chemical/intervention ontology terms: CHEBI:2682 amphotericin B; CHEBI:75291 miltefosine; CHEBI:2955 azithromycin; CHEBI:46081 fluconazole; CHEBI:28077 rifampicin; NCIT therapeutic hypothermia; NCIT ventriculostomy/CSF shunt.

13. Prevention

Prevention is primarily behavioral and environmental — there is no vaccine for human use.

• Primary prevention: keep water out of the nose during warm-freshwater activities; use nose clips or hold the nose when jumping/diving; avoid stirring up sediment in warm shallow water (CDC guidance).
• Nasal irrigation & ablution safety: use only sterile, distilled, or previously boiled-and-cooled water in neti pots / sinus-rinse devices, and for religious ablution (wudu) where tap water may be under-chlorinated (22919000 21291600).
• Water-system control: adequate chlorination/disinfection of pools and splash pads; proper design/operation of treated recreational water venues (40146665).
• Secondary prevention: clinician awareness for early recognition of PAM in meningoencephalitis with freshwater exposure → faster diagnosis/treatment (40146665 26582886).
• Public-health measures: environmental water surveillance (PCR/LAMP), outbreak investigation, and public education in endemic/warm regions (25822175).
• Immunization: experimental DNA vaccine against nfa1 induces protective Th1/Th2 immunity in mice — no human vaccine (22955499).

14. Other Species / Natural Disease

• Agent taxonomy: Naegleria fowleri, NCBI Taxon:5763 (Heterolobosea, Percolozoa).
• Host range / experimental hosts: Mice are the standard experimental host and develop a disease resembling human PAM after intranasal inoculation (646016 669800).
• Natural disease in cattle (Bos taurus, NCBI Taxon:9913): A documented outbreak killed nine 10–20-month-old Holstein heifers in California (summers 1998–1999) that drank untreated warm surface water (>42 °C); autopsy showed necrosuppurative hemorrhagic meningoencephalitis with olfactory lobes/nerves most severely affected, N. fowleri confirmed by IHC and culture — "the disease in cattle closely resembles primary amoebic meningoencephalitis in humans" (16475525). This establishes PAM as a genuine naturally occurring cross-species disease sharing route of entry, climate dependence, and pathology. Veterinary relevance: include Naegleria meningoencephalitis in summer bovine CNS differentials in hot regions.
• Zoonotic potential: None in the classic sense — not transmitted animal-to-human or human-to-human; acquisition is strictly environmental (waterborne via nose). (Rare iatrogenic concern: organ-transplant transmission from infected donors — 24279908.)
• Comparative biology: non-pathogenic congener N. gruberi and related Willaertia magna share some virulence-gene homologs but lack full pathogenicity, enabling comparative virulence studies (31797948 33843581).

15. Model Organisms

• Mouse (BALB/c, others): the principal in vivo model; intranasal inoculation reproduces olfactory-nerve invasion and lethal meningoencephalitis (646016 669800). Used to study innate (neutrophil) defense, protective immunity, passive immunization, and DNA vaccination (2628288 2486833 22955499).
• Phenotype recapitulation: high — mirrors route of entry, CNS pathology, rapid lethality, and sex/age-dependent susceptibility (females and older mice more resistant; 669800).
• Limitations: dose/route differences (IV vs intranasal), accelerated course, and species differences in immune response.
• In vitro / cellular models: co-culture with human fibrosarcoma cells, MDCK epithelial cells, and primary nasal epithelial cells to dissect contact-dependent trogocytosis and EV-mediated cytopathy (40096149 40312759).
• Omics models: axenic vs brain-passaged trophozoite proteomics/transcriptomics and secretome/EV proteomics for virulence-factor discovery (40096149 39735262 33843581).
• Resources: ATCC strains of N. fowleri; CDC Free-Living and Intestinal Amebas Laboratory (surveillance, PCR, strain archiving).

Evidence Source Legend

Human clinical/epidemiologic: 32369575 26582886 42764041 41873284 40146665 27123690 23621053 22919000 23710088 35020127 25667249 26679626 27525348 24279908 21291600 39780139. In vitro/mechanistic: 40096149 40312759 39432113 32716210 40016342 36839446 39735262. Experimental therapeutics (in vitro/preclinical): 32970675 38835258. Model organism (mouse): 646016 669800 2628288 2486833 22955499. Natural animal disease (veterinary): 16475525. Genomics/phylogenomics: 33843581 31797948 39826589.

Supported vs Refuted Hypotheses

Supported: (1) PAM is a pathogen-caused infectious disease with no human causal gene (etiology = N. fowleri). (2) Exposure is overwhelmingly warm-freshwater nasal entry with olfactory-nerve CNS invasion. (3) Disease is >95–97% fatal, predominantly in young males. (4) Cytopathy is dual — contact-dependent actin/food-cup trogocytosis plus contact-independent EV/pore-forming/protease cytolysis. (5) Non-recreational tap-water routes (ablution, neti-pot) are real and epidemiologically important. (6) PAM occurs as a natural cross-species disease (cattle) and is well modeled in intranasally-inoculated mice. Refuted / not applicable: Any human Mendelian inheritance, susceptibility/protective loci, ClinVar variants, chromosomal abnormalities, genetic testing, carrier screening, or genetic counseling role — none exist for this infectious disease. Person-to-person and classic zoonotic animal-to-human transmission are not supported (acquisition is strictly environmental; rare iatrogenic transplant risk aside).

Limitations & Future Directions

Evidence is dominated by rare case reports and pooled surveillance (no RCTs; survivorship anecdotal). Optimal drug regimen and the independent contribution of hypothermia remain undefined. Priorities: validated early rapid diagnostics (point-of-care PCR/LAMP), new amebicidal drugs crossing the blood–brain barrier, and climate-driven surveillance as the amoeba's geographic range expands.