Experimental Sarcocystis hominis infection in cattle: lesions and ultrastructure of sarcocysts.

Five calves inoculated orally with 10(5)-10(6) sporocysts of Sarcocystis hominis from human feces were necropsied 10, 18, 24, 111, and 222 days postinoculation (DPI). Calves became febrile (greater than 40-41 C) between 10 and 24 DPI and developed mild anemia (packed cell volumes were reduced by 40% of initial values) between 29 and 57 DPI but otherwise remained clinically normal. Focal hepatitis, mesenteric lymphadenitis, and myocarditis were seen in calves at 10, 18, and 24 DPI. No stages of the parasite were found at any of these times except for a few merozoites in macrophages associated with myocardial lesions in the calf necropsied 24 DPI. Mature sarcocysts at 111 and 222 DPI were up to 950 microm long and their walls were up to 6 microm thick. They were found only in skeletal muscles. One immature sarcocyst was seen in the myocardium of the calf at 222 DPI.