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Acanthamoeba species

Disease. Acanthamoebic infection, Acanthamoebic keratitis, Granulomatous amoebic encephalitis

Geographic distribution. Worldwide distribution

Infection rate. Acanthamoebic keratitis known to be closely associated with contact lens wearing was reported more commonly in industrialized countries than developing or under-developed countries. The number of case report has been rapidly increasing in last decade. Granulomatous amoebic encephalitis occurs rarely and small number of cases were reported.

Life cycle. Trophozoites do active functions in favorable environments and become cysts in less favorable environment for survival. Acanthamoeba has wide distribution in soil, fresh water, sea water, etc. Some species show facultative parasitism in mammals and in several vertebrates, fish and presumably other animals.

Morphology. Acanthamoeba trophozoites (25-40 ㎛) are quite large compared to other protozoa. The most typical trait is the needle-like projections called acanthopodia for movement. Cytoplasm contain numerous mitochondria, vesicles, phagocytic and pinocytic vacuoles, ribosomes and other organells. The cyst diameter varies a great deal (15 to 28 ㎛) and the cyst wall appears as a two-layer membrane: the outer wall (exocyst) is moderately undulated, while the endocyst shows a typically polygonal arrangement.

Pathology and clinical symptoms. Most of GAE patients are immuno-compromised individuals. The infection is insidious in onset and with a prolonged clinical course. Altered mental status, headache, and stiff neck are prominent symptoms. In the case of keratitis, the infection remains confined to the cornea. It is suspected in patients who have corneal ulcer which do not respond to the usual medications and in patients who are contact lens wearer.

Diagnosis. Corneal biosy and corneal scrapings and culture usually permit the correct diagnosis.

Prevention. Regular boiling of contact lens and storage cases.

Comments. Most cases of granulomatous amoebic encephalitis were diagnosed by postmortem autopsy.

Hyun-Hee Kong