Amoebic meningoencephalitis caused by Balamuthia mandrillaris in an orang utan.

Objective: To describe a case of meningoencephalitis caused by Balamuthia mandrillaris in an orang utan.

Design: A pathological case report.

Animal: A 20 years old male orang utan (Pongo pygmaeus).

Procedure: The disease process was investigated by clinical pathology, necropsy, histopathology and immunofluorescence labelling.

Results: The orang utan developed sudden onset of depression, lethargy, inappetence and apparent head pain. The condition was considered to be related to a 2 year history of upper and lower respiratory disease, and the animal was placed on antibiotics after extensive testing. By the seventh day the animal had become ataxic and disoriented and a brain abscess was suspected. He died on the ninth day of illness. At necropsy, and subsequent sectioning, the brain showed multiple circular, soft, white to grey brown areas of varying size, the largest being in the left temporal (3.5 cm diameter) and right occipital (2.5 cm diameter) regions of the cerebrum. Histological examination of these regions revealed many amoebic trophozoites and occasional cysts associated with areas of haemorrhage and inflammatory necrosis. The trophozoites were packed in perivascular spaces and their nuclei often contained two or more prominent nucleoli. Immunofluorescent labelling of histological sections suggested that the agent was B mandrillaris.

Clinical Implications: This report provides further evidence that B mandrillaris, a free living amoeba, can act as a pathogen in animals as well as people, and cause fatal meningoencephalitis. Along with Naegleria and Acanthamoeba spp, B mandrillaris should be considered amongst the causes of acute onset meningoencephalitis in animals.