Babesia bigemina vaccine: comparison of the efficacy and safety of Australian and South African strains under experimental conditions in South Africa.

A Babesia bigemina vaccine strain (G strain) of reduced virulence was obtained from Australia and tested experimentally for efficacy and virulence. The strain caused mild reactions in 10 animals and afforded good protection to challenge with a virulent South African strain. The virulence of the local vaccine strain was not noticeably reduced after 3 slow passages in intact calves and it was consequently replaced by the Australian strain in the Onderstepoort babesiosis vaccine.