Serosurveillance and factors associated with the presence of antibodies against bluetongue virus in dairy cattle in two eco-zones of Nepal.

Cattle play an important role in the epidemiology of bluetongue (BT) by acting as reservoir hosts. However, the status of BT virus (BTV) in dairy cattle in Nepal is unknown. The objective of this study was to estimate the prevalence of BTV antibodies in dairy cattle in two eco-zones of Nepal, and to identify the factors associated with virus exposure. The authors conducted a cross-sectional serosurvey from March 2012 through February 2013 by sampling 131 dairy cattle from seven clusters (villages) in the Chitwan district in the Terai region (southern lowlands) and the Lamjung district in the Hills region (the middle part of Nepal). Of the 131 serum samples tested, 29.3% (95% confidence interval [CI]: 21.5-37.2) were positive for BTV antibodies. Herd-level seroprevalence was 45.7% (95% CI: 30.9-61.0). Bivariate analysis indicated a positive association between seroconversion to BTV and age, and an association with breed of cattle after controlling for clustering of animals within herds. Based on this model, cattle were more likely to become seropositive as they aged. Crossbred cattle were more likely to be seropositive than those of exotic breeds (odds ratio [OR] = 4.6; 95% CI: 1.5-14.1). The results indicate widespread exposure of dairy cattle to BTV in Nepal. The authors suggest that dairy cattle should be included in the surveillance plan for BTV infection in Nepal and that it is important to educate farmers about the possible impacts of this disease.