Clinical Features:
Acute primary amebic meningoencephalitis (PAM) is caused by Naegleria fowleri.  It presents with severe headache and other meningeal signs, fever, vomiting, and focal neurologic deficits, and progresses rapidly (<10 days) and frequently to coma and death.  Acanthamoeba spp. causes mostly subacute or chronic granulomatous amebic encephalitis (GAE), with a clinical picture of headaches, altered mental status, and focal neurologic deficit, which progresses over several weeks to death.  In addition, Acanthamoeba spp. can cause granulomatous skin lesions and, more seriously, keratitis and corneal ulcers following corneal trauma or in association with contact lens use.  Non-contact lens users and contact lens users with safe lens care practices can become infected.  However, poor contact lens hygiene and exposure to contaminated water may increase the risk among contact lens users.

Laboratory Diagnosis:
In Naegleria infections, the diagnosis can be made by microscopic examination of cerebrospinal fluid (CSF).  A wet mount may detect motile trophozoites, and a Giemsa-stained smear will show trophozoites with typical morphology.  In Acanthamoeba infections, the diagnosis can be made from microscopic examination of stained smears of biopsy specimens (brain tissue, skin, cornea) or of corneal scrapings, which may detect trophozoites and cysts.  Confocal microscopy or cultivation of the causal organism, and its identification by direct immunofluorescent antibody, may also prove useful.  An increasing number of PCR-based techniques (conventional and real-time PCR) have been described for detection and identification of free-living amebic infections in the clinical samples listed above.  Such techniques may be available in selected reference diagnostic laboratories.

Diagnostic findings

• Microscopy
• Molecular Methods

Treatment:
Eye and skin infections caused by Acanthamoeba spp. are generally treatable.  For additional information on treatment of Acanthamoeba keratitis, see the recommendations in The Medical Letter (Drugs for Parasitic Infections). Although most cases of brain (CNS) infection with Acanthamoeba have resulted in death, some patients have recovered from the infection with proper treatment.  Amphotericin B* has been successfully used in some cases to treat PAM caused by Naegleria fowleri.  For additional information on treatment of amebic meningoencephalitis, see the recommendations in The Medical Letter (Drugs for Parasitic Infections).

*This drug is approved by the FDA, but considered investigational for this purpose.

References

1. Visvesvara GS. Pathogenic and Opportunistic Amebae. In: Murray PR, Baron EJ, Jorgensen JH, Landry ML, Pfaller MA, editors. Manual of Clinical Microbiology. 9th ed. Washington DC: ASM Press; 2007. p. 2082-91.
2. Visvesvara GS, Moura H and Schuster FL. Pathogenic and opportunistic free-living amoebae: Acanthamoeba spp., Balamuthia mandrillaris, Naegleria fowleri, and Sappinia diploidea. FEMS Immunol Med Micribiol 2007;50(1):1-26.
3. Marciano-Cabral F, Cabral G. Acanthamoeba spp. as agents of disease in humans. Clin Microbiol Rev 2003;16(2):273-307.