Development of babesial vaccines.

The most widely used vaccine against cattle babesiosis was blood from a carrier animal. The development of a calf passage attenuated strain in Australia was a great improvement in vaccine safety and efficacy. The degree of immunity generated by this vaccine remains a standard against which to compare other vaccines. Vaccines derived from culture supernatants have also been developed. These have considerable value. To date no efficacious recombinant vaccine exists. A variety of antigens will probably be required in any synthetic vaccine. Study of clones derived from calf passage attenuated vaccines indicate that the vaccine contains a variety of parasites of differing virulence. The attenuation process enriches for the less virulent clones. The clones may also vary in their antigenic characteristics. To date no single clone gives immunity equal to the original uncloned preparation. An ideal vaccine should not be a living agent. It will probably contain a variety of antigens and may induce less strong immunity than the living vaccine but its greater safety, stability and ease of handling will more than compensate for this.