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Primary Amebic Meningoencephalitis


Richard D. Pearson

, MD, University of Virginia School of Medicine

Last full review/revision Nov 2020| Content last modified Nov 2020
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Primary amebic meningoencephalitis is a rare, usually fatal, acute central nervous system (CNS) infection caused by Naegleria fowleri.

Naegleria fowleri inhabit bodies of warm fresh water worldwide. Swimming in contaminated water exposes nasal mucosa to the organism, which can enter the CNS via olfactory neuroepithelium and the cribriform plate. Most patients are healthy children or young adults.

Symptoms and Signs

Symptoms of primary amebic meningoencephalitis begin within 1 to 2 weeks of exposure, sometimes with alteration of smell and taste. Fulminant meningoencephalitis ensues, with headache, meningismus, and mental status change, progressing to death within 10 days, usually due to cerebral herniation. Only a few patients have survived.


  • Cerebrospinal fluid examination

Primary amebic meningoencephalitis is suspected based on history of swimming in fresh water, but confirmation is difficult because CT and routine cerebrospinal fluid (CSF) tests, although necessary to exclude other causes, are nonspecific.

Wet mount of fresh, not refrigerated or frozen, CSF should be done; it may demonstrate motile amebic trophozoites (which can be seen in Giemsa-stained specimens but are destroyed by Gram stain techniques).

Immunohistochemistry, amebic culture, polymerase chain reaction of CSF, and/or brain biopsy are available in specialized reference laboratories. Consultation with the Centers for Disease Control and Prevention (CDC) or other experts in the diagnosis of amebic encephalitis is recommended.


  • Multiple drugs, including miltefosine plus antifungal drugs and antibiotics

Optimal treatment is unclear, but it must be started as soon as possible. Consultation with experts at the CDC is recommended (call the CDC Emergency Operations Center at 770-488-7100).

A regimen should include miltefosine, an antileishmanial drug, which has been used in combination with other drugs in the successful treatment of patients with primary amebic meningoencephalitis. Miltefosine has also been used successfully to treat encephalitis due to Balamuthia and Acanthamoeba. Miltefosine is now available commercially.

Other antimicrobial drugs that have been used in combination treatment regimens for Naegleria include

  • Amphotericin B

  • Rifampin

  • An azole (fluconazole, voriconazole, or ketoconazole)

  • Azithromycin

Key Points

  • Primary amebic meningoencephalitis is rare, usually fatal.

  • The infection is acquired when swimming in contaminated fresh water; Naegleria fowleri enters the CNS via olfactory neuroepithelium and the cribriform plate.

  • Diagnostic tests should include a wet mount and Giemsa-stained specimen of CSF.

  • Treat the infection with multiple antimicrobial drugs, including miltefosine; if needed, treat seizures and cerebral edema with antiseizure drugs and dexamethasone.

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