Development of a Babesia bovis live attenuated vaccine.

Babesia bovis is the blood parasite causing the highest morbidity and mortality of cattle in Cuba. Thus a control program based on immunization with a vaccine using an attenuated strain of the parasite was developed. For this purpose, a virulent B. bovis strain was isolated and then attenuated by the traditional method in which biological characteristics, proteolytic activity and vector transmissibility were studied. The protection conferred by the vaccine was measured by vaccinating cattle which then was challenged with a heterologous strain. In order to assess postvaccination accident risks, 2603 cattle were vaccinated and those showing clinical signs of babesiosis were treated. A study of cost-benefit was performed in a herd where frequent outbreaks of babesiosis occurred; prevalence and clinical case incidence in vaccinated and nonvaccinated animals were determined. Vaccinated animals survived to challenge whereas two control animals died. In 2% of the vaccinated animals less than 6 months of age, postvaccination accidents occurred, whereas in older animals this index was higher (p < 0.001). The cost-benefit study showed a rate of approximately $10 pesos (national currency) for each peso invested due to the high mortality caused by the parasite. Until an effective, killed vaccine is available, vaccination with live vaccines is advantageous to prevent bovine babesiosis.