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Key Features

Essentials of Diagnosis

  • A fulminating, hemorrhagic, necrotizing meningoencephalitis

  • Occurs in healthy children and young adults and is rapidly fatal

General Considerations

  • Caused by free-living amoebae

    • Naegleria fowleri (most commonly)

    • Balamuthia mandrillaris

    • Acanthamoeba species

  • The incubation period varies from 2 to 15 days


  • N fowleri is a thermophilic organism found in

    • Fresh and polluted warm lake water

    • Domestic water supplies

    • Swimming pools

    • Thermal water

    • Sewers

  • Most patients give a history of exposure to warm fresh water

Clinical Findings

Symptoms and Signs

  • Early symptoms include headache, fever, stiff neck, and lethargy, often associated with rhinitis and pharyngitis

  • Vomiting, disorientation, and other signs of meningoencephalitis develop within 1 or 2 days, followed by coma and then death within 7–10 days

Differential Diagnosis

  • No distinctive clinical features distinguish the infection from acute bacterial meningoencephalitis


Laboratory Tests

  • Cerebrospinal fluid (CSF) shows hundred to thousands of leukocytes and erythrocytes per cubic millimeter

  • Protein is usually elevated, and glucose is normal or moderately reduced

  • A fresh wet mount of the CSF may show motile trophozoites

  • Staining with Giemsa or Wright stain will identify trophozoites

  • Species identification is based on morphology and immunologic methods



  • Amphotericin B is drug of choice

  • Four survivors in North America were treated with amphotericin B, rifampin, and other agents



  • Nearly always fatal

When to Admit

  • All patients with confirmed or suspected disease


Bravo  FG  et al. Balamuthia mandrillaris infection of the skin and central nervous system: an emerging disease of concern to many specialties in medicine. Curr Opin Infect Dis. 2011 Apr; 24(2):112–7.
[PubMed: 21192259]  
Grace  E  et al. Naegleria fowleri: pathogenesis, diagnosis, and treatment options. Antimicrob Agents Chemother. 2015 Nov;59(11):6677–81.
[PubMed: 26259797]  
Lorenzo-Morales  J  et al. An update on Acanthamoeba keratitis: diagnosis, pathogenesis and treatment. Parasite. 2015;22:10.
[PubMed: 25687209]  
Siddiqui  R  et al. Primary amoebic meningoencephalitis caused by Naegleria fowleri: an old enemy presenting new challenges. PLoS Negl Trop Dis. 2014 Aug 14;8(8):e3017.
[PubMed: 25121759]

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