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.