GENOTYPIC DIVERSITY IN-FIELD ISOLATES OF BABESIA-BOVIS FROM CATTLE WITH BABESIOSIS AFTER VACCINATION

Objective To determine whether particular genotypes of Babesia bovis w ere common to field isolates obtained from cattle properties in Queens land where the B bovis vaccine had apparently failed. Design A compara tive study of polymerase chain reaction genotypes in different populat ions of B bovis. Procedure Two polymerase chain reaction assays were a pplied to analyse DNA extracts of B bovis vaccine (K, T and Dixie stra ins) and 27 field isolates from 24 properties where disease outbreaks had occurred despite the use of the vaccine. To evaluate the stability of the genotypes identified, 11 of the field isolates were inoculated into experimental cattle that had either been previously vaccinated w ith T strain or not vaccinated. Results No particular genotype of B bo vis was responsible for the problems observed in previously vaccinated herds. None of the isolates had genotypes identical to the vaccine st rains used. No geographic trends among the genotypes were observed. Is olates that originated from the same property also had different genot ypes. Blood passage of the 11 field isolates in either previously vacc inated or nonvaccinated cattle did not alter the original genotype. Co nclusion No particular genotypes identified by the Bv80 and BvVA1 poly merase chain reaction assays could be associated with vaccine failures .