Bovine babesiosis: induction of protective immunity with culture-derived Babesia bovis and Babesia bigemina immunogens.

The comparative protective efficacy of culture-derived Babesia bovis and B. bigemina immunogens against challenge exposure of susceptible crossbred cattle to heterologous strains was examined and correlated with the antigenic threshold requirements for induction of protective immunity. Strong protection was observed in animals vaccinated with 10 ml-equivalent doses of soluble, B. bovis exoantigen-containing supernatant fluids. Similar protective responses to B. bigemina exoantigens were evident even at 1 ml-equivalent dosages. In addition, the efficacy of a combined B. bovis-B. bigemina immunogen was assessed with a dose-response analysis in highly susceptible, purebred cattle. Vaccinated animals were protected against clinical babesiosis, and significant weight gains were recorded after challenge infection with virulent parasites.