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
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.
Eye and skin
infections caused by Acanthamoeba spp. are generally treatable. 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
*This drug is
approved by the FDA, but considered investigational for this purpose.
- 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.
- Visvesvara GS, Moura H and Schuster FL. Pathogenic and
opportunistic free-living amoebae: Acanthamoeba spp., Balamuthia
mandrillaris, Naegleria fowleri, and Sappinia diploidea. FEMS Immunol
- Marciano-Cabral F, Cabral G. Acanthamoeba spp. as agents
of disease in humans. Clin Microbiol Rev 2003;16(2):273-307.