Class-specific antibody responses in cattle following experimental challenge with sporocysts or merozoites of Sarcocystis cruzi

An ELISA using antigen produced from merozoites of Sarcocystis cruzi was developed to monitor specific IgM and IgG antibody, following challenge of cattle with either merozoites or sporocysts of S. cruzi. This assay was compared with an ELISA using antigen produced from the cystozoite stage of the parasite. Both ELISAs were able to detect significant increases in levels of circulating IgM and IgG antibodies against Sarcocystis in all challenged cows; however, the magnitude of the titres was greater in the ELISA which used the antigen derived from the merozoites. This immunoassay also detected increases in the levels of IgG earlier than did the assay using antigen derived from cystozoites of S. cruzi. Since this rise coincided with the presence of clinical signs, and was persistent for several weeks, the IgG-ELISA using antigen derived from merozoites appears to be suitable for the diagnosis of acute sarcocystiosis in cattle. Furthermore, since significant increases in the levels of circulating IgM and IgG antibodies against Sarcocystis were detected in the cows infected with merozoites of S. cruzi, it is evident that merozoites of S. cruzi cultured in vitro maintain their capability to replicate in the natural intermediate host