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 w as developed to monitor specific IgM and IgG antibody, following chall enge of cattle with either merozoites or sporocysts of S. cruzi. This assay was compared with an ELISA using antigen produced from the cysto zoite stage of the parasite. Both ELISAs were able to detect significa nt increases in levels of circulating IgM and IgG antibodies against S arcocystis in all challenged cows; however, the magnitude of the titre s was greater in the ELISA which used the antigen derived from the mer ozoites. 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 sign s, and was persistent for several weeks, the IgG-ELISA using antigen d erived from merozoites appears to be suitable for the diagnosis of acu te sarcocystiosis in cattle. Furthermore, since significant increases in the levels of circulating IgM and IgG antibodies against Sarcocysti s were detected in the cows infected with merozoites of S. cruzi, it i s evident that merozoites of S. cruzi cultured in vitro maintain their capability to replicate in the natural intermediate host. (C) 1997 El sevier Science B.V.