Seroprevalence investigation of bovine ephemeral fever in yaks in Tibetan Plateau of China from 2012 to 2015.

Bovine ephemeral fever (BEF) is caused by the arthropod-borne bovine ephemeral fever virus (BEFV), which is classified in family Rhabdoviridae and genus Ephemerovirus. However, it is still unclear whether yaks from the Tibetan plateau of China are exposed to BEFV. It is the first time that a survey was conducted to investigate the seroprevalence of BEFV infection in yaks (Bos grunniens) on the Tibetan Plateau of China. A total of 1123 serum samples were collected randomly from yaks from 2012 to 2015 and were assayed for BEFV antibodies by enzyme-linked immunosorbent assay (ELISA). The proportions of positive serum samples were assessed among the 1123 samples, as well as factors of geographical origin and years. The results showed that there were 454 serum samples that tested positive for BEFV, and the total positive rate is 40.4 %. The prevalence in 2012, 2013, 2014, and 2015 was 49.3, 36, 44.1, and 34.0 %, respectively, and the difference is statistically significant (P< 0.01). In different regions, the prevalence was ranged from 34.7 to 45.7 % with a significant difference among the different regions of (P < 0.05). Logistic regression analysis showed that yaks in Tibet (Xizang autonomous region) (45.7 %) had 1.6 times (OR = 1.589, 95 % CI = 1.141-2.215, P < 0.01) higher risk of being seropositive compared to yaks in Qinghai province, while no regional difference was found of Sichuan province compared to Qinghai (P > 0.05). The prevalence in 2012 (49.3 %) was more than 1.8 time (OR = 1.880, 95 % CI = 1.350-2.619, P < 0.001) at risk of acquiring the infection compared to the year of 2015. The prevalence of yaks in 2014 (44.1 %) had a 1.5 times (OR = 1.528, 95 % CI = 1.350-2.619, p < 0.001) at risk of being seropositive compared to yaks in 2015, while no year difference was found of 2013 compared to 2015 (P > 0.05). Our study suggests that the yaks from the high plateau are highly infected by BEFV, and geographical origin and years are main risk factors for BEF seroprevalence.