Amebic meningoencephalitis

Sith Sathornsumetee MD (Dr. Sathornsumetee of Mahidol University, Thailand, has no relevant financial relationships to disclose.)
Karen L Roos MD FAAN, editor. (Dr. Roos of Indiana University School of Medicine has no relevant financial relationships to disclose.)
Originally released January 12, 1994; last updated February 6, 2017; expires February 6, 2020

This article includes discussion of amebic meningoencephalitis, amebic meningitis, cerebral amebiasis, and granulomatous amebic encephalitis. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.


Infection of the central nervous system caused by amoebae is rare but usually lethal. The etiologic agents include Acanthamoeba, Naegleria, Balamuthia mandrillaris, Sappinia pedata, and Paravahlkampfia francinae n sp. Early diagnosis and prompt treatment with multiple antimicrobial agents are important in attempting to reduce mortality. In this article, the author reviews the recent surveillances and provides an update on treatment options for amebic meningoencephalitis.

Key points


• Primary amebic meningoencephalitis represents a rare but usually fatal infection.


• Diagnosis is based on high clinical suspicion. Demonstration of motile trophozoites in CSF may be helpful for Naegleria fowleri infection. However, routine CSF findings in Acanthamoeba and Balamuthia infection are usually nonspecific. Immunodetection or polymerase chain reaction-based diagnostics may be helpful for diagnosis but are not widely available.


• Early treatment with combinations of antimicrobial agents, including miltefosine, may save lives and improve outcome.


• If primary amebic meningoencephalitis is suspected, the U.S. Centers for Disease Control and Prevention should be contacted (770-488-7100) for discussion of rapid diagnosis and treatment.

Historical note and terminology

Systemic infection of Entamoeba histolytica resulting in meningoencephalitis has been recognized for many years. Legrand first summarized a series of 45 cases in 1912 (Legrand 1912). More recently, the concept of primary amebic meningoencephalitis has been described (Fowler and Carter 1965). The main etiologic agents of primary amebic meningoencephalitis are Naegleria and Acanthamoeba (Robert and Rorke 1973). In addition, Balamuthia mandrillaris, previously termed “Leptomyxid ameba” (Visvesvara et al 1990) and Sappinia diploidea (Gelman et al 2003) have been implicated as rare causes of primary amebic meningoencephalitis in humans. At this time, fewer than 500 human cases of primary amebic meningoencephalitis have been reported in the clinical literature worldwide.

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