Acanthamoeba spp. are free-living amebae that inhabit a variety of air, soil, and
water environments. However, these amebae can also act as opportunistic as well as
nonopportunistic pathogens. They are the causative agents of granulomatous amebic
encephalitis and amebic keratitis and have been associated with cutaneous lesions
and sinusitis. Immuno compromised individuals, including AIDS patients, are particularly
susceptible to infections with Acanthamoeba. The immune defense mechanisms that operate
against Acanthamoeba have not been well characterized, but it has been proposed that
both innate and acquired immunity play a role. The ameba's life cycle includes an
active feeding trophozoite stage and a dormant cyst stage. Trophozoites feed on bacteria,
yeast, and algae. However, both trophozoites and cysts can retain viable bacteria
and may serve as reservoirs for bacteria with human pathogenic potential. Diagnosis
of infection includes direct microscopy of wet mounts of cerebrospinal fluid or stained
smears of cerebrospinal fluid sediment, light or electron microscopy of tissues, in
vitro cultivation of Acanthamoeba, and histological assessment of frozen or paraffin-embedded
sections of brain or cutaneous lesion biopsy material. Immunocytochemistry, chemifluorescent
dye staining, PCR, and analysis of DNA sequence variation also have been employed
for laboratory diagnosis. Treatment of Acanthamoeba infections has met with mixed
results. However, chlorhexidine gluconate, alone or in combination with propamidene
isethionate, is effective in some patients. Furthermore, effective treatment is complicated
since patients may present with underlying disease and Acanthamoeba infection may
not be recognized. Since an increase in the number of cases of Acanthamoeba infections
has occurred worldwide, these protozoa have become increasingly important as agents
of human disease.