Bovine babesiosis: the immunization of cattle with fractions of erythrocytes infected with Babesia bovis (syn B. argentina).

Soluble antigen which protected susceptible cattle against challenge with Babesia bovis was extracted from B. bovis-infected erythrocytes by sonic disintegration and separation of the soluble from the insoluble matter by ultracentrifugation. The material was then fractionated by the precipitation of fibrinogen-like proteins. The precipitate contained the babesial antigens that were located on the stroma of the infected erythrocytes. Antigen originally located on the parasite remained in solution. Both fractions conferred protection on splenectomized calves against challenge with B. bovis. However, the fraction containing the parasite antigens appeared to have more potential for development as a killed vaccine because it was not heavily contaminated with antigenic material from bovine erythrocytes.