Treatment of Naegleria fowleri Infection (Primary Amoebic Meningoencephalitis)
Immediately initiate a multi-drug regimen including miltefosine, amphotericin B (both intravenous and intrathecal), fluconazole, rifampin, and dexamethasone upon clinical suspicion—do not wait for confirmatory testing, as this infection has a >95% mortality rate with death typically occurring within 5 days if untreated. 1
Critical Treatment Principles
Start treatment on suspicion alone. The diagnosis is confirmed pre-mortem in only 27% of cases, and waiting for definitive diagnosis is a fatal error. 1 The disease mimics bacterial meningitis but does not respond to standard antibiotics, making early recognition and immediate specific therapy the only chance for survival. 2, 1
Specific Multi-Drug Regimen
The optimal treatment protocol includes: 1
- Miltefosine (oral): This agent is essential and has been associated with the only recent survivors of this previously uniformly fatal disease 1, 3
- Amphotericin B: Both intravenous AND intrathecal administration 1, 4
- Fluconazole (intravenous) 1, 4
- Rifampin (intravenous) 1, 4
- Dexamethasone: For management of cerebral edema 1, 4
Aggressive Supportive Care
Manage elevated intracranial pressure using traumatic brain injury protocols. Survival has been attributed to aggressive management of intracranial pressure in addition to antimicrobial therapy. 3 The patient will likely develop severe cerebral edema, which is the primary cause of death. 2
Key Clinical Pitfalls to Avoid
Do not treat as bacterial meningitis alone. The most common fatal error is misdiagnosing PAM as bacterial meningitis and treating only with antibiotics, which are completely ineffective against this amoeba. 1
Do not delay treatment for confirmatory testing. Given the 5-day median time to death and the extremely high mortality rate exceeding 95%, empiric treatment must begin immediately when PAM is suspected based on clinical presentation and exposure history. 5, 2, 1
Diagnostic Clues That Should Trigger Immediate Treatment
Suspect PAM and start treatment immediately in any patient with: 2, 1
- Rapidly progressive meningoencephalitis unresponsive to antibiotics
- Recent freshwater exposure (swimming in warm lakes, hot springs) during summer months 1
- Nasal water exposure through neti pots, ritual nasal ablution, or lawn water slides 2
- Change in taste or smell 2-5 days after water exposure 2
- CSF showing pleocytosis but negative bacterial cultures
Examine fresh CSF immediately for motile trophozoites—this is the most critical diagnostic step, though treatment should not be delayed if this is negative. 1
Rare but Important Complication
Monitor for diabetes insipidus. Although rare, DI has been reported as a complication with poor outcomes, presenting as massive urine output (300-500 mL/hour) and hypernatremia. 4 If this develops, treat with desmopressin while continuing the anti-amoebic regimen. 4
Prognosis Context
Despite optimal therapy, the mortality rate remains >95%. 5, 2, 6 However, the few documented survivors in North America all received early multi-drug therapy including miltefosine, aggressive intracranial pressure management, and both IV and intrathecal amphotericin B. 3 This makes immediate recognition and treatment initiation the only modifiable factor that can impact survival.