Apparent transmission efficiency of Culicoides sonorensis (Diptera: Ceratopogonidae) for epizootic hemorrhagic disease virus serotype 2 in white-tailed deer (Odocoileus virginianus)

Epizootic hemorrhagic disease virus (EHDV) is transmitted by Culicoides biting midges (Diptera: Ceratopogonidae) to numerous ruminant species and is a significant pathogen of white-tailed deer (WTD; Odocoileus virginianus). In North America, the only confirmed vector of EHDV is Culicoides sonorensis, although other Culicoides species are suspected vectors. Previous experimental infections have demonstrated Culicoides-to-WTD transmission of EHDV, but little is known about transmission efficiency. Our objective was to determine if the bite from as few as 5 EHDV-infected C. sonorensis is sufficient to infect a WTD. Colonized C. sonorensis were intrathoracically inoculated with EHDV-2, held for 10 days at 26 °C to allow for virus replication, and were then given the opportunity to feed on susceptible WTD (n = 2): deer A, 10 midges; deer B, 5 midges. After feeding, Culicoides were processed individually for virus. All Culicoides were positive by virus isolation except 1 midge from deer B, suggesting the inoculation failed in that midge. Deer were observed twice daily and sampled on 0, 4, 7, 11, and 14 days post feeding (dpf). Culicoides feeding was variable: deer A, only 1/10 midges fed and only took a partial blood meal but 4 additional probe sites were observed on the skin; deer B, 5/5 midges blood fed (1 partial, 4 to repletion) with a total of 5 bite sites observed. Both deer developed viremia and mild clinical disease. Infection of WTD with EHDV-2 by the bite of 1 to 4 C. sonorensis demonstrates EHDV-2 transmission efficiency and the potential importance of probing.