Serological Survey of Bovine Viral Diarrhoea Virus among Yaks (Bos poephagus grunniens) in Hongyuan of Sichuan, China

Totally, 516 bloods were achieved from the coccygeal or jugular vein of yaks during 2012 to 2014 in Hongyuan with the northern latitudes and eastern longitudes of this region is 31°51′-33°19′ and 101°51′-103°23′, respectively with an average altitude of 3600 m and an average annual temperature of 1.1°C. Serums were separated by employing centrifugation at 3,000×g for 20 min, and then stored at -20°C until further analysis (Li et al., 2017).

Serum samples were tested for antibodies (Ab) against BVDV with highly conserved p80 protein of pestiviruses of a commercial indirect ELISA kit (IDEXX BVDV Total Ab, USA), under the guidance of the manufacturer’s instructions. When S/P value ≤ 0.20 was classified as negative for BVDV Ab and ≥ 0.20 but ≤ 0.30 was considered suspected and the assay should be retested. Additionally, the OD value of average control was considered negative if the value was ≤ 0.250. Samples with S/P values ≥ 0.30 were considered as positive for BVDV Ab.

Statistical analysis was calculated be employing chi-square test with Statistical Analysis System (SPSS; Version 18.0). Uni-variate logistic regression analysis was preformed to determine the significantly associated variable with BVDV antibodies and to identify potentail risk factors by calculating odds ratios (OR) and 95% CI. The difference was recognized to be statistically significant when P<0.05.

In the current study, the prevalence of BVDV were detected to be 51.7% (257/516; 95% CI: 47.3-56.1) (Table I). 51.1% (95% CI: 46.5-55.6) in the adult yaks and 60.5% (95% CI: 43.4-76.0) in calves, respectively (Table I). Though, BVDV is initially isolated from cattle, it can infect other animal species including pig, sheep, goat and even wild animals through crossing the species barrier, which bring out obvious economic losses (Ames, 2005). Scott et al. (2013) found that the seroprevalence of BVDV was 71% and 40% in South African kudu and Namibian eland, respectively. Mishra et al. (2009) reported an overall prevalence of 23.4% and 16.9% of this disease in sheep and goats in India, respectively. Previously, Casaubon et al. (2012) and Albayrak et al. (2013) reported BVDV infected Swiss wild ruminants (1.7%) and in northern Turkey wild boar (5.4%). The possible reasons of the prevalence difference in different areas could be manifold, as different areas located in different geographical with a different climate and environment, which may influence the presence of BVDV (Li et al., 2015). Importantly, BVDV infection rate of 30.4% in Bactrian camels was reported in western china (Gao et al., 2013b). On Qinghai-Tibetan plateauIn, inhabit numerous of wild animals, such as chiru, white lipped deer, argali, Bactrian camels and free ranging yaks ensuring ample opportunity for BVDV cross-species transmission. Although, scarce knowledge about the infection of BVDV in wild animals (except Bactrian camels) on this plateau, the current presented high infection rates demonstrated that this common ecological niche was thought to be a possible avenue of BVDV infection.

The infection rate of BVDV in current study differs from that found in other epidemiologic surveys on the Qinghai-Tibetan Plateau. A report published by Gao et al. (2013a) elaborated 53.65% and 72.14% in Tibet and Qinghai, respectively. The possible reasons of BVDV prevalence varies among same plateau could be that the herd size and breeding managements were changing with time. The BVDV infection rate in 2012 to 2014 was 45.3% (95% CI: 38.6%-52.1%); 56.0% (95% CI: 49.7-62.2) and 60.5% (95% CI: 43.4-76.0), respectively with a significant difference in the three years (P<0.05) (Table I). Actor of year was demonstrated to be risk factor influencing the prevalence significantly. In different years, yaks in 2013 (56.0%) presented over 1.5 times (OR=1.542; 95% CI=1.074-2.214, P<0.05) higher risk of infection by comparison with yaks in 2012 (45.3%%); while yaks in 2014 (60.5%) no significant difference was found compared yaks in 2012 (P>0.05) (Table I). In other studies, Gao et al. (1999) and Xue et al. (2010) reported that BVDV infection rate in yak herds by the neutralization test was 38.46% and 42.3% in Sichuan, respectively. These observations indicate that number of yaks infecting BVDV were rapid increasing and widespread in Sichuan

a, there was a significant difference of the prevalence of BVDV in yaks among different years (P<0.05, χ2=6.791).

and should be aroused the concern of the local government and the appropriate measures should be taken to control the disease. There was no difference in the prevalence in yaks of different ages, as the prevalence of BVDV infection in the younger yaks was not significantly different with that in adult ones (P>0.05), though, Thomson (1991) published that BVDV was commonly isolated from diarrheic calves aging less than 2 months in Colorado.

In conclusion, a high prevalent (51.7%) of BVDV infection in yaks and a growing trend of BVDV infection in yaks was discovered in this area. Infections with BVDV in yak populations may have a negative impact on health and welfare, also may transmit this varus to other wild animals on the high plateau. Therefore, BVDV control programs should also be considered planning.

The current research was founded by Key Science Fund of Science and Technology Agency of Tibet Autonomous Region and projects in the National Science & Technology Pillar Program during the 12th Five-year Plan Period (2012BAD3B03).

Authors have declared no conflict of interest.