BALAMUTHIA-MANDRILLARIS, NG, N-SP, AGENT OF AMEBIC MENINGOENCEPHALITIS IN HUMANS AND OTHER ANIMALS

We recently reported the isolation of a leptomyxid ameba from the brai n of a mandrill baboon that died of meningoencephalitis. Based on ligh t and electron microscopic studies, animal pathogenicity tests, and im munofluorescence patterns, we conclude that our isolate differs fundam entally from the other two amebas (Leptomyxa and Gephyramoeba) include d in the Order Leptomyxida. We therefore created a new genus. Balamuth ia, to accommodate our isolate and described it as Balamuthia mandrill aris to reflect the origin of the type species. Briefly, B. mandrillar is is a pathogenic ameba that causes amebic encephalitis in humans and animals. It has trophic and cyst stages in its life cycle, and is uni nucleate with a large vesicular nucleus and a central nucleolus. Matur e cysts have a tripartite wall consisting of an outer loose ectocyst, an inner endocyst and a middle mesocyst. Unlike Acanthamoeba and Naegl eria, the other two amebas that cause amebic encephalitis in humans, B alamuthia will not grow on agar plates seeded with enteric bacteria. H owever, Balamuthia grows on a variety of mammalian cell cultures and k ills mice following intranasal or intraperitoneal inoculation. Based o n immunofluorescence testing, 35 cases of amebic encephalitis in human s and three in other animals have been identified worldwide as being c aused by Bulamuthia.