Abstract
Balamuthia mandrillaris is a newly described free-living amoeba capable of causing fatal meningoencephalitis in humans and animals. Because the number of human cases is rapidly increasing, this infection is now considered an important emerging disease by the medical community. A retrospective review of the pathology database for the Zoological Society of San Diego (the San Diego Zoo and San Diego Wild Animal Park) for the period July 1965 through December 1994 revealed five cases of amoebic meningoencephalitis, all in Old World primates. The infected animals were a 3-year, 10-month-old female mandrill (Papio sphinx), from which the original isolation of B. mandrillaris was made, a 5-year-old male white-cheeked gibbon (Hylobates concolor leucogenys), a 1-year-old female western lowland gorilla (Gorilla gorilla gorilla), a 13-year, 5-month-old male western lowland gorilla, and a 6-year-old female Kikuyu colobus monkey (Colobus guereza kikuyuensis). Two different disease patterns were identified: the gibbon, mandrill, and 1-year-old gorilla had an acute to subacute necrotizing amoebic meningoencephalitis with a short clinical course, and the adult gorilla and colobus monkey had a granulomatous amoebic meningoencephalitis with extraneural fibrogranulomatous inflammatory lesions and a long clinical course. Indirect immunofluorescent staining of amoebas in brain sections with a Balamuthia-specific polyclonal antibody was positive in all five animals. Indirect immunofluorescent staining for several species of Acanthamoeba, Naegleria fowlel, and Hartmanella vermiformis was negative. Direct examination of water and soil samples from the gorilla and former mandrill enclosures revealed unidentified amoebas in 11/27 samples, but intraperitoneal inoculations in mice failed to induce disease. Attempts to isolate amoebas from frozen tissues from the adult male gorilla were unsuccessful.