Culture-derived Babesia orientalis exoantigens used as a vaccine against buffalo babesiosis.

Buffalo babesiosis represents a major problem for the livestock industry in China. The pathogen of this disease was isolated and identified as Babesia orientalis and subsequently propagated in vitro, using the microaerophilus stationary phase culture system. The aim of this study was to determine the efficacy of exoantigens derived from B. orientalis cultures to induce a protective immunity against challenge exposure to virulent organisms in laboratory and field. The results showed that exoantigens of B. orientalis could induce a high degree of protection against challenge with a virulent B. orientalis strain. The animals in the vaccinated group exhibited a slight decrease in haemoglobin levels and blood cell counts, whereas animals in the control group showed typical clinical symptoms and died between days 11 and 16 after challenge. In another approach, 82 buffaloes kept in B. orientalis-endemic areas were injected with exoantigens plus Freund's adjuvant in two doses at an interval of 2 weeks, one month before the endemic period. An additional 86 buffaloes served as unvaccinated controls. During the endemic period, the clinical signs of all buffaloes were monitored and the antibody response was investigated, using the latex agglutination test. During the endemic period, none of the vaccinated buffaloes showed clinical signs or died, whereas five control buffaloes showed clinical signs and two of them died. The mean antibody titre of vaccinated animals was higher than that of the control animals. These results showed that the culture-derived exoantigens of B. orientalis could be used as a vaccine to prevent buffalo babesiosis.