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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 amebas

    • Naegleria fowleri (most commonly)

    • Balamuthia mandrillaris

    • Acanthamoeba species

  • The incubation period varies from 2 to 15 days

Demographics

  • 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

Diagnosis

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

Treatment

Medications

  • Amphotericin B is drug of choice

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

Outcome

Prognosis

  • Nearly always fatal

When to Admit

  • All patients with confirmed or suspected disease

References

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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.
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Grace  E,  et al. Naegleria fowleri: pathogenesis, diagnosis, and treatment options. Antimicrob Agents Chemother. 2015 Nov;59(11):6677–81.
[PubMed: 26259797]  
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Lorenzo-Morales  J,  et al. An update on Acanthamoeba keratitis: diagnosis, pathogenesis and treatment. Parasite. 2015;22:10.
[PubMed: 25687209]  
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Schuster  FL,  et al. Under the radar: Balamuthia amebic encephalitis. Clin Infect Dis. 2009 Apr 1; 48(7):879–87.
[PubMed: 19236272]  
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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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Visvesvara  GS. Amebic meningoencephalitides and keratitis: challenges in diagnosis and treatment. Curr Opin Infect Dis. 2010 Dec;23(6):590–4.
[PubMed: 20802332]  

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