First report of Babesia bigemina infection in white yaks in China.

White yaks, a unique yak breed and the pearl of the plateau, only live in Tianzhu Tibetan Autonomous County (TTAC), Gansu Province, northwest China, contributing significantly to local economy. However, there was no information on the prevalence of Babesia bigemina in white yaks. In this study, a total of 974 serum samples collected from white yaks in TTAC were examined for specific antibodies against B. bigemina using a commercially available ELISA kit. The overall seroprevalence of B. bigemina in white yaks was 17.76% (173/974). A multivariate logistic regression analysis was performed to determine the risk factors associated with B. bigemina seroprevalence, and the results indicated that age, gender and the numbers of pregnancies of white yaks were not the significant risk factors. However, the white yaks in spring (OR=3.523, 95% CI=1.899-6.538, P<0.001) and summer (OR=3.439, 95% CI=1.909-6.193, P<0.001) encountered higher risk of being exposed to B. bigemina than that in winter. Thus, season was considered as a risk factor associated with B. bigemina infection. This is the first survey of B. bigemina seroprevalence in white yaks in China, which extends the host range for B. bigemina and provides useful information for controlling B. bigemina infection in white yaks.