Sarcocystis suihominis and S. bovihominis are ingested as bradyzoites from cysts in infected pork and beef ( Pathology, Figs. 7, 8, and 9). There is no schizogony in the human gut. The ingested bradyzoites develop directly into gametocytes in the lamina propria; then fertilization occurs, followed by development of a zygote and an oocyst. Sporulation takes place in the gut wall, with 2 sporocysts, each forming 4 sporozoites. Judging from a few isolated observations, where, however, the possibility of the presence of other pathogen could not be excluded, there may be intense mixed inflammatory reaction that includes eosinophils. Experimental infections suggest the absence of a strong immune reaction, and the possible hypersensitivity reactions, resulting in the greater pathogenicity of S. suihominis than of S. bovihominis. Sporulated sporocysts are usually shed in the feces and appear to be infectious only to pigs (S. suihominis) or cattle (S. bovihominis). In...