FIELD-EVALUATION OF AN EXOANTIGEN-CONTAINING BABESIA VACCINE IN VENEZUELA

Bovine babesiosis is endemic in Venezuela, causing significant losses in highly susceptible imported cattle. Current immunoprophylactic meth ods include the less desirable use of live parasites. Inactivated vacc ines derived from exoantigen-containing supernatant fluids of in vitro Babesia bovis and B. bigemina cultures have been developed and consti tute a major improvement in vaccine safety, stability and ease of hand ling. Vaccination trials conducted under field conditions provide the final evalutation of a culture-derived B. bovis-B. bigemina vaccine. D uring a 5-year period, approximately 8,000 cattle were vaccinated and 16 clinical trials carried out in. 7 states of Venezuela. Clinical, se rologic and parasitologic data were collected monthly from 10% of the animals over a 2-year period. Data were also collected from a similar number of nonvaccinated control cattle. Analysis of results from these trials demonstrated a reduction in the incidence of clinical disease among vaccinated animals and complete protection against mortality cau sed hy babesiosis. Vaccine efficacy was measured calculating the incid ence rates of disease and mortality among vaccinated and nonvaccinated cattle. Use of this inactivated vaccine offers the best combination o f safety, potency and efficacy for the effective immunoprophylactic co ntrol of bovine babesiosis.