ENCEPHALOMYELITIS DUE TO A SARCOCYSTIS NEURONA-LIKE PROTOZOAN IN A RHESUS-MONKEY (MACACA-MULATTA) INFECTED WITH SIMIAN IMMUNODEFICIENCY VIRUS

A captive-born rhesus monkey (Macaca mulatta) experimentally infected with simian immunodeficiency virus developed neurologic abnormalities approximately seven months postinoculation. A chronic necrotizing ence phalomyelitis with intralesional protozoal schizonts was diagnosed his tologically. The protozoa was identified as Sarcocystis neurona based on its morphologic characteristics by light and electron microscopic e xamination, the developmental stages of the schizonts, and positive st aining with antisera against Sarcocystis cruzi by immunocytochemical t echniques. 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 encepha lomyelitis in horses, raccoons, and mink.