Pathology, immunohistochemistry, and ultrastructural findings associated with neurological sarcocystosis in cattle

Paraffin-embedded blocks of brain of a nine months old bull calf that died of neurological signs in 1982 in Germany were restudied. Numerous schizonts and merozoites were found associated with extensive but focal necrosis and severe meningoencephalitis. Developing stages of schizonts as well as free merozoites were identified. The schizonts were primarily in perivascular areas. Ultrastructurally, schizonts were seen both in capillaries and in extravascular space. Merozoites were often concentrated in adventitial layers of capillaries. Schizonts divided by endopolygeny, the nucleus became multi-lobed, and at the terminal stage nuclear lobes were incorporated into budding merozoites. Individual merozoites were seen in neurons, astrocytes, oligodendrocytes, leukocytes, and vascular endothelial cells. Occasionally merozoites were present in the nucleus of mononuclear cells. Individual merozoites were ovoid, 3-5×2-3μm in size, and contained a prominent nucleus, numerous micronemes, a conoid, but no rhoptries. Schizonts and merozoites did not react to polyclonal rabbit Neospora caninum, Toxoplasma gondii, and Sarcocystis neurona antibodies but did react to Sarcocystis cruzi antibodies. Because of morphological characteristics and the type of lesions, the parasite was likely due to an unidentified Sarcocystis species, different from S. cruzi.