Primary Amebic Meningoencephalitis
- Primary amebic meningoencephalitis is a rare central nervous system disease caused by the thermophilic free-living amoeba Naegleria fowleri
- The amoeba lives in freshwater and can enter the brain through the cribriform plate after water containing it enters the nose; the amoeba causes direct tissue damage with hemorrhage and necrosis of brain tissue 
- Exposure can occur from natural water sources (lakes, ponds, puddles) as well as man-made sources (swimming pools)
- Cases nearly always result in death - in the USA 141/145 known cases were fatal
- >50% cases in the USA occur in Texas and Florida
- Often diagnosed post-mortem given general low clinical suspicion and rapid death of patients
- Lumbar puncture - basic studies may be consistent with meningitis with a negative Gram stain
- Wet mount may see free moving trophozoites
- Giemsa-Wright, H+E, PAS, trichrome staining may show amoebae
- Immunohistochemical staining
- PCR of CSF or tissue sample are newer modalities
- CT brain - should be to evaluate for abscess/mass/hemorrhage and prior to LP
- Anti-amoeba therapy (CDC recommendations at: https://www.cdc.gov/parasites/naegleria/treatment-hcp.html)
- Amphotericin B: 1.5mg/kg/day divided in 2 doses for 3 days followed by 1mg/kg/day IV as one dose for 11 days
- Intrathecal Amphotericin B: 1.5mg once daily for 2 days followed by 1mg/day every other day for 8 days
- Azithromycin: 10mg/kg/day once daily IV/PO for 28 days, max dose 500mg/day
- Fluconazole: 10mg/kg/day once daily IV/PO for 28 days, max dose 600mg/day
- Rifampin: 10mg/kg/day once daily IV/PO for 28 days, max dose 500mg/day
- Miltefosine: 50mg PO BID (<45kg) or TID (>45kg) for 28 days
- Dexamethasone: 0.6mg/kg/day IV for 4 days
- Therapeutic hypothermia
- Elevated ICP management
- Infectious disease consultation
- Admission to ICU
- Very few patients have made a full neurologic recovery; key factors are high clinical suspicion and prompt diagnosis, aggressive anti-amoeba therapy, and management of elevated ICP
- Marciano-Cabral F et al. The immune response to Naegleria fowleri amebae and pathogenesis of infection. FEMS Immunol Med Microbiol. 2007;51(2):243-259.
- Yoder JS et al. The epidemiology of primary amoebic meningoencephalitis in the USA, 1962–2008. Epidemiol Infect. 2010;138:968-975.
- Gharpure R et al. Epidemiology and Clinical Characteristics of Primary Amebic Meningoencephalitis Caused by Naegleria fowleri: A Global Review. CID. 2019. https://doi.org/10.1093/cid/ciaa520.
- Linam et al. Successful Treatment of an Adolescent With Naegleria fowleri Primary Amebic Meningoencephalitis. Pediatrics. 2015;135(3):e744-e748.
- Cope et al. Use of the Novel Therapeutic Agent Miltefosine for the Treatment of Primary Amebic Meningoencephalitis: Report of 1 Fatal and 1 Surviving Case. CID. 2016;62(6):774-776.