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Objective: To demonstrate the value of PCR assays to determine the genotypes of Babesia bovis in cattle with clinical signs of babesiosis within 3 weeks after vaccination against tick fever., Design: Samples from 5 cases of babesiosis in cattle soon after vaccination against tick fever were analysed in two PCR assays., Procedure: Parasite DNA was purified from blood taken from cattle with signs of babesiosis within 3 weeks of vaccination against tick fever. DNA was also prepared from the tissues of animals that died of babesiosis. Two PCR assays that amplify repeat sequences of DNA within the B bovis genes, Bv80 and BvVA1, were used to differentiate the genotypes of field isolates and vaccine strains of B bovis., Results: One of the five cases of babesiosis was found to be caused by a vaccine strain, but PCR analyses showed that the predominant isolate in the other four cases was not the vaccine strain., Conclusions: PCR assays on the DNA of B bovis obtained from the blood or tissues of cattle clinically affected with tick fever within 3 weeks after vaccination are useful to distinguish between vaccine strains and field isolates as the source of infection.

Objective: To determine whether particular genotypes of Babesia bovis were common to field isolates obtained from cattle properties in Queensland where the B bovis vaccine had apparently failed., Design: A comparative study of polymerase chain reaction genotypes in different populations of B bovis., Procedure: Two polymerase chain reaction assays were applied to analyse DNA extracts of B bovis vaccine (K, T and Dixie strains) 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 with T strain or not vaccinated., Results: No particular genotype of B bovis was responsible for the problems observed in previously vaccinated herds. None of the isolates had genotypes identical to the vaccine strains used. No geographic trends among the genotypes were observed. Isolates that originated from the same property also had different genotypes. Blood passage of the 11 field isolates in either previously vaccinated or nonvaccinated cattle did not alter the original genotype., Conclusion: No particular genotypes identified by the Bv80 and BvVA1 polymerase chain reaction assays could be associated with vaccine failures.