Blocking Babesia bovis vaccine reactions of dairy cattle in milk.

The use of 1.16 mg/kg (one third) of the recommended dose of diminazene aceturate, administered indiscriminately to cattle on day seven of the unfrozen Babesia bovis and Babesia bigemina bivalent live blood vaccine reaction, was an infection and block treatment method of immunisation used successfully with no known adverse effect on the parasites or the development of protective immunity. Continuing with this practice after replacement of the unfrozen vaccine with deep-frozen monovalent B. bovis and B. bigemina live blood vaccines resulted in reports of vaccine failure. Laboratory investigation indicated the harmful effect of block treatment in preventing the development of durable immunity against B. bigemina as opposed to the much lesser effect it had on B. bovis. Consequently the practice was no longer recommended. A B. bovis vaccination attempt aimed at controlling the disease of dairy cows in milk (n = 30) resulted in 20% fatalities during the expected vaccine reaction period. The practice of block treating B. bovis was therefore reinvestigated, this time in a field trial using dairy cattle in milk (n = 11). Using 0.88 mg/kg (one quarter) of the recommended dose of diminazene administered on day 12 of the B. bovis vaccine reaction resulted in only two animals (n = 5) testing ≥ 1/80 positive with the indirect fluorescent antibody test (IFAT) although parasites could be demonstrated in three. In the untreated control group, by contrast, five of the vaccinated animals (n = 6) tested ≥ 1/80 positive with IFAT and parasites could be demonstrated in all. The unsatisfactory outcome obtained in this study, combined with that of the earlier investigation, indicated that there are more factors that influence successful vaccination than previously considered. It is therefore concluded that block treatment of the live frozen South African cattle babesiosis vaccines reactions is not recommended.

Serological survey of Babesia bovis and Babesia bigemina in cattle in South Africa.

A total of 719 serum samples collected from clinically healthy cattle from eight provinces located in different districts of South Africa were examined by the indirect enzyme-linked immunosorbent assay (ELISA) and the standard indirect fluorescent antibody test (IFAT) to determine the serological prevalence of Babesia bovis and Babesia bigemina. The results showed that 35.3% and 39.7% of cattle were positive for B. bovis and 30% and 36.5% were positive for B. bigemina antibodies on ELISA and IFAT, respectively. Mixed infections were detected in 18.2% and 26.3% of the samples using ELISA and IFAT, respectively. Consequently, the ELISAs with recombinant B. bovis spherical body protein-4 (BbSBP-4) and B. bigemina C-terminal rhoptry-associated protein-1 (BbigRAP-1/CT) were proven to be highly reliable in the serological diagnoses of bovine babesiosis in South African cattle, as evidenced by the significant concordance rates when the results were compared to those of IFAT. Moreover, the serological prevalence was significantly different among the tested provinces, in which the ranges exhibited between 15% and 73% for B. bovis infection and between 13% and 54% for B. bigemina infection. High sero-positive rates were present in Mpumalanga and KwaZulu-Natal provinces, while the lowest rate was in the North West province. Our data provide important information regarding the current seroprevalence of bovine babesiosis in South Africa, which might be beneficial in developing rational strategies for disease control and management.