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Key Features

Essentials of Diagnosis

  • Acute meningoencephalitis: fever, headache, meningism, acute mental deterioration

  • Chronic granulomatous encephalitis: insidious onset of focal neurologic deficits

  • Keratitis: pain, photophobia, conjunctivitis, blurred vision

General Considerations

  • Acute meningoencephalitis

    • Occurs mostly in children and young adults

    • Caused by Naegleria fowleri

      • Found in warm fresh water and moist soil

      • Infection is associated with swimming in warm freshwater lakes and using contaminated tap water for nasal irrigation

    • CNS invasion occurs after nasal inoculation of N fowleri which travel along the olfactory nerves via the cribiform plate to the brain

  • Chronic granulomatous encephalitis

    • Caused by Acanthamoeba or Balamuthia

    • Can occur in immunocompotent patients

    • Occurs more commonly in immunocompromised patients

    • No association with freshwater swimming

  • Acanthamoeba keratitis is a corneal infection associated with minor trauma or use of soft contact lenses in otherwise healthy persons

Clinical Findings

  • Acute meningoencephalitis

    • Abrupt fever

    • Headache

    • Nausea and vomiting

    • Disturbances in smell and taste

    • Meningismus

    • Decreased mental status a few days to 2 weeks after exposure

  • Chronic granulomatous encephalitis

    • Insidious onset of focal neurologic deficits

    • Headache is presenting symptom in about 50% of patients

    • Skin, sinus, or lung infections with Acanthamoeba precede many of the CNS infections and may still be present at the onset of neurologic disease

  • Acanthamoeba keratitis

    • Usually follows an indolent course

    • May resemble herpes simplex or bacterial keratitis initially

    • Delay in diagnosis is associated with worse outcomes


  • Acute meningoencephalitis

    • Cerebrospinal fluid (CSF) is usually hemorrhagic, with leukocyte counts that may be normal early but later range from 400 to 2600/mL with neutrophil predominance, low to normal glucose, and elevated protein

    • Diagnosis relies on finding trophozoites on a wet mount of the CSF

    • Immunofluorescent and polymerase chain reaction (PCR)–based diagnostic assays are available through the Centers for Disease Control and Prevention (CDC)

  • Granulomatous encephalitis

    • Brain biopsy of CT-identified nonenhancing lucent areas is diagnostic

    • CSF is usually nondiagnostic with a lymphocytic pleocytosis, mild to severe elevation of protein (> 1000 mg/dL), and normal or low glucose

    • Acanthamoeba and Balamuthia amoebas have only rarely been found in the CSF; however, they can be visualized in brain biopsies or grown from brain or other infected tissues

    • Immunofluorescent and PCR-based diagnostic assays are available through the CDC

  • Acanthamoeba keratitis

    • Trophozoites found in corneal scrapings

    • Parasite is isolated from corneal specimens or contact lens cultures


  • Acute amebic meningoencephalitis caused by N fowleri

    • High-dose intravenous amphotericin B with the possible addition of miconazole and rifampin

    • Azithromycin may be tried as an adjuvant

  • Balamuthia encephalitis: combination of flucytosine, pentamidine, fluconazole, sulfadiazine, and a macrolide has been reported successful

  • Acanthamoeba encephalitis should be treated with a combination of pentamidine, an azole, flucytosine, and sulfadiazine

  • Miltefosine is an investigational new drug with in vitro activity against free-living ameba which has become available for treatment through ...

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