Characterization of the antibody response in birds following infection with wild-type and attenuated strains of Eimeria tenella and Eimeria necatrix.

Live vaccines containing attenuated parasite strains are increasingly used to control chicken coccidiosis. In this paper antibody responses elicited by infections with wild-type and attenuated strains of Eimeria tenella and E.necatrix were characterized by immunoblotting and ELISA with homologous and heterologous antisera. Few differences between antisera from birds infected with wild and attenuated strains of E. tenella were evident in immunoblots conducted with merozoite antigen preparations from both E. tenella strains, however the reactivity of sera raised in birds infected with the wild-type strain was noticeably more intense. In ELISAs conducted with merozoite antigen preparations, antisera from birds infected with the wild-type strains of E. tenella and E. necatrix consistently produced a significantly higher (P < 0.05) antibody response than antisera from birds infected with the attenuated strains. Likewise, avidity ELISAs conducted with the E. tenella strains demonstrated that antibodies in birds infected with the wild-type strain were of significantly higher avidity (P < 0.05) than antibodies in birds infected with the attenuated strain. The differences in the antibody responses are probably due to changes in the attenuated strain as a result of selection for precocious development and the less severe tissue damage and inflammation of the intestine resulting from infection with the attenuated strain.