Encephalomyelitis Due to a Sarcocystis Neurona-Like Protozoan in a Rhesus Monkey (Macaca Mulatta) Infected with Simian Immunodeficiency Virus

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  • Yerkes Regional Primate Research Center and Department of Pathology, Emory University, Parasite Biology and Epidemiology Laboratory, Livestock and Poultry Sciences Institute, Agricultural Research Service, U.S. Department of Agriculture, Atlanta, Georgia
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A captive-born rhesus monkey (Macaca mulatta) experimentally infected with simian immunodeficiency virus developed neurologic abnormalities approximately seven months postinoculation. A chronic necrotizing encephalomyelitis with intralesional protozoal schizonts was diagnosed histologically. The protozoa was identified as Sarcocystis neurona based on its morphologic characteristics by light and electron microscopic examination, the developmental stages of the schizonts, and positive staining with antisera against Sarcocystis cruzi by immunocytochemical techniques. Although S. neurona may be confused with Toxoplasma gondii by light microscopy, the former lacks rhoptries, is in direct contact with the host cell cytoplasm, and divides by endopolygeny. Sarcocystis neurona has recently been identified as an etiologic agent of encephalomyelitis in horses, raccoons, and mink.