Vaccination of cattle against B. bovis infection with live attenuated parasites and non-viable immunogens.

Susceptible dairy cattle were immunized with attenuated, live calf-derived, in vitro-cultured or biologically cloned Babesia bovis, with non-viable exoantigens, or with recombinant rhoptry-associated protein 1 (rRAP1). Antibody response assessed by the indirect fluorescent assay (IFA) and by the growth inhibition activity in vitro showed that seroconversion correlated with neutralization activity in vitro in all immunized groups, but not with protective immunity in vivo. The protective responses elicited by immunization with completely avirulent biologically cloned live parasites, or by the exoantigens were sufficient for highly susceptible dairy cattle, in which prime immunization with blood-derived attenuated parasites cause clinical babesiosis. Upon challenge with virulent live parasites all immunized calves were solidly protected, but only partial protective immunity was acquired by rRAP1 immunization.