Amoebic meningoencephalitis in a sheep.

A case of amoebic meningoencephalitis in a sheep, suspected of being caused by Acanthamoeba sp., is described. An adult ewe was necropsied 5 days after it had developed anorexia and nervous signs, which included ataxia and walking in circles. Significant gross lesions were restricted to the central nervous system and consisted of thickening of the meninges and extensive necrosis of the cerebrum and cerebellum. The cerebral changes were characterised microscopically by a multifocal to coalescent necrotising granulomatous meningoencephalitis as well as choroid plexitis, ventriculitis and diffuse vasculitis. Numerous amoebic trophozoites and a few encysted forms morphologically compatible with Acanthamoeba sp. were present in the affected areas, particularly in the walls of blood vessels and perivascular spaces.