The Epidemiology of Bluetongue Virus in Mnisi, South Africa

The role of cattle in the epidemiology of bluetongue (BT) as well as the distribution of different vector species throughout South Africa is not well understood. Mnisi, a rural area located in Mpumalanga, South Africa, was selected for an epidemiological study. The prevalence of Culicoides species associated with this area as well as whether bluetongue virus (BTV) is circulating in the area is unclear. Sera were collected from 1 260 cattle and screened with a BTV-specific cELISA. Light traps operated during autumn and winter periods. Midges were identified to species level, pooled (n = 200) and screened for BTV RNA with a real-time RT-qPCR. Blood samples from seronegative cattle were also screened for BTV RNA. Antibodies specific to BTV were detected in 95.7% of the sera with a statistical significant difference (p < 0.05) between age groups and villages. Twenty-five different Culicoides species were identified of which C. imicola was the most abundant. Bluetongue virus RNA was detected in 51.2% (autumn) and 75.9% (winter) of the midges collected. A total of 35.5% seronegative cattle tested positive for the presence of BTV RNA. These results demonstrate that BTV as well as different vectors are circulating in the