Meningoencephalitis and brain abscess due to a free-living amoeba.

A 47-year-old diabetic woman developed fatal meningoencephalitis due to a free-living amoeba. The responsible organism appeared to be neither Naegleria nor Acanthamoeba-Hartmannella. Both acute and chronic (granulomatous) inflammatory reactions of the brain were present, and both cysts and trophozoite forms were readily visualized. The latest classification and methods of identification of such amoebae are reviewed and their threat to public health underscored. It should be realized that a variety of free-living amoebae exist in nature, which potentially can produce meningoencephalitis in humans, and that none of these organisms should be labeled or considered as "avirulent" or "nonpathogenic" until proved otherwise.