Improved rates of in vitro excystation of sporozoites from sporocysts of Sarcocystis capracanis, Sarcocystis cruzi, and Sarcocystis tenella were obtained by pretreating sporocysts with an aqueous sodium hypochlorite (NaOCl) solution followed by incubation in excysting fluid (EF). After pretreatment with NaOCl, sporocysts were washed 4 times in Hanks' balanced salt solution and then incubated in various EF (pH 7.4) at 38.5 C in 5% CO2-95% air. Maximum rates of excystation (free sporozoites/(sporozoites in sporocysts + free sporozoites) X 100) for all 3 species of Sarcocystis occurred at 4 hr after incubation in EF. These rates were 17% for S. capracanis after incubation in EF containing 2% trypsin + 10% caprine bile; 90% for S. cruzi in 2% trypsin + 10% bovine bile; and 20% for S. tenella in 2% trypsin + 10% caprine bile. Only a 40% excystation rate occurred in sporocysts of S. cruzi that had been stored previously for 14 days in aqueous potassium dichromate. Excysted sporozoites of S. capracanis, S. cruzi, and S. tenella penetrated and developed to mature meronts in bovine pulmonary artery endothelial cells or bovine monocytes.

Sporozoites and culture-derived merozoites of Sarcocystis cruzi were used to elicit monoclonal antibodies (MAb's) in mice. Some of these antibodies reacted with the surface of live sporozoites and merozoites as determined by immunofluorescence. An array of similar antigens was identified in Western blots of sporozoites by both anti-merozoite MAb's and an anti-sporozoite MAb. At least 1 antigen in blots of bradyzoites was identified by anti-merozoite MAb's and a cluster of antigens was identified by an anti-sporozoite antibody. These results indicate that several surface epitopes of sporozoites and merozoites are shared with molecules of bradyzoites and that antigen patterns of molecules bearing these epitopes in 3 stages of Sarcocystis may be either distinct or similar.