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 [1]
  • 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[2][3]

Clinical Features

Differential Diagnosis


  • 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
    • Culture
  • PCR of CSF or tissue sample are newer modalities
  • CT brain - should be to evaluate for abscess/mass/hemorrhage and prior to LP



  • 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

See Also

External Links


  1. 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.
  2. Yoder JS et al. The epidemiology of primary amoebic meningoencephalitis in the USA, 1962–2008. Epidemiol Infect. 2010;138:968-975.
  3. Gharpure R et al. Epidemiology and Clinical Characteristics of Primary Amebic Meningoencephalitis Caused by Naegleria fowleri: A Global Review. CID. 2019.
  4. Linam et al. Successful Treatment of an Adolescent With Naegleria fowleri Primary Amebic Meningoencephalitis. Pediatrics. 2015;135(3):e744-e748.
  5. 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.