The main objective of the study was to investigate whether there were significant differences in prevalence of antibodies to Babesia bigemina and Babesia bovis between vaccinated and unvaccinated cattle in a tick-borne disease endemic area of South Africa. The study was carried out between August 2000 and June 2001, in the Northern Province of South Africa at Nooitgedacht ranch (24° 33’ S and 28° 36’ E), where calves were vaccinated against B. bigemina and B. bovis infections, and at Vlakplaas ranch (24° 58’ S and 28° 05’ E), where calves had not been vaccinated against these parasites. Sera were collected from cattle of different age groups at both ranches and the presence of antibodies against B. bigemina and B. bovisdetermined using the indirect fluorescent antibody (IFA) test. It was found that B. bovis was absent from both ranches while B. bigemina antibody was more prevalent in cattle at Vlakplaas (unvaccinated) than at Nooitgedacht (vaccinated). The difference in B. bigemina antibody response between the ranches may have been due to variations in tick populations. Vlakplaas, which had been operated for 14 years with relaxed tick control, probably had sufficient numbers of vector ticks for frequent transmission and maintenance of endemic stability to B. bigemina. At Nooitgedacht, however, livestock farming had been interrupted for three years before it was resumed in 1999 and it is postulated that the tick population had been substantially reduced due to lack of hosts to a level insufficient for the establishment and maintenance of endemic stability to B. bigemina. The vaccinated cattle and breeding cows might therefore have lost IFA reacting antibody titres due to low levels of superinfections. The findings show that an endemically stable situation to B. bigemina could be achieved by adapting a tick control method that allows sufficient number of ticks on cattle rather than relying entirely on intensive tick control and vaccination. Therefore, it may not be necessary to vaccinate calves against B. bigemina on ranches located in B. bigemina-endemic areas and stocked with Bos indicus cattle or their crosses. Key words: Babesia bigemina, Babesia bovis, bovine babesiosis, tick-borne diseases, endemic stability, immunization, antibody response, Brahman, Bonsmara, South Africa.
Dissertation (MSc (Veterinary Sciences))--University of Pretoria, 2001.