ABSTRACT

Free-living amoebae include Acanthamoeba species, Naegleria fowleri, Balamuthia mandrillaris and Sappinia diploidea. In contrast to the parasitic amoebae, free-living amoebae are not welladapted for a parasitic lifestyle, as they almost invariably kill their hosts. Additionally, as freeliving in nature, these amoebae are not dependent on a host for transmission or spread. Human infection is produced by several species of Acanthamoeba, of which A. astronyxis, A. castellani, A. culbertsoni and A. polyphaga are the most common. Only one species, Naegleria fowleri, causes a fulminating meningoencephalitis, while B. mandrillaris has been associated with encep - halitis in both immunocompromised and immunocompetent individuals. A single case report of S. diploidea encephalitis in an immunocompetent male has been documented.