Epidemiological insights into bovine viral diarrhea virus and bovine rotavirus in diarrheic Yaks on the Qinghai-Tibet Plateau.

Diarrhea is common in yak calves and causes substantial economic losses to the yak industry on the Qinghai-Tibet Plateau. Bovine viral diarrhea virus (BVDV) and bovine rotavirus (BRV) are important enteric pathogens in cattle, but their epidemiology and potential association in yaks remain unclear. In this study, 1,623 fecal samples were collected from yaks across different locations, age groups, seasons, and breeds to investigate BVDV, BRV, and BVDV/BRV dual positivity. Viral positivity was detected using PCR amplification, and associated factors were analyzed using chi-square tests and multivariable binary logistic regression. Overall, 277 samples were positive for BVDV, 224 for BRV, and 92 for both viruses, corresponding to positivity rates of 17.07%, 13.80%, and 5.67%, respectively. BVDV positivity differed significantly among seasons (P = 0.0008), with a lower rate in summer than in spring and winter, and was strongly associated with BRV positivity (P < 0.0001). BRV positivity differed significantly by location, age, season, and breed in univariable analyses, and was higher in adult yaks than in calves (16.54% vs. 11.35%, P = 0.0025) but lower in summer than in spring and winter. Multivariable analysis showed that BRV status was the only factor associated with BVDV positivity (OR = 4.277, 95% CI: 3.121-5.861, P < 0.001), whereas age, sampling location, and BVDV status were associated with BRV positivity, with BVDV-positive yaks showing a markedly higher risk of BRV positivity (OR = 4.299, 95% CI: 3.138-5.889, P < 0.001). No factor was significantly associated with BVDV/BRV dual positivity. These findings indicate that BVDV and BRV circulate among yaks and are strongly associated, suggesting possible viral interaction or shared exposure conditions and highlighting the need for integrated surveillance and control strategies targeting multiple viral pathogens.