Application of PCR assays to determine the genotype of Babesia bovis parasites isolated from cattle with clinical babesiosis soon after vaccination against tick fever

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