Vector competence parameters of Culicoides variipennis (Diptera: Ceratopogonidae) for bluetongue virus serotype 2

Culicoides variipennis (Coquillett), the only proven vector of bluetongue virus (BLU) in the western hemisphere, was evaluated as a vector of bluetongue virus serotype 2 (BLU 2). This serotype was isolated from sentinel cattle in south Florida at a site devoid of C. variipennis. Culicoides variipennis readily fed on a mixture of defibrinated blood and BLU 2 through chicken skin membrane. An infection rate of 46.2% was obtained. A growth curve of virus titers recovered from orally infected flies showed a linear relationship between the virus titers and the period of extrinsic incubation. Culicoides variipennis also became infected when inoculated intrathoracically with BLU 2. Peak titers were higher and more rapidly attained in inoculated flies when compared with orally infected flies. Infected C. variipennis also transmitted BLU 2 to sheep via bite. These results demonstrate that C. variipennis is a potential biological vector of BLU 2 in the laboratory. The implication of this on the epidemiology of BLU 2 in the United States is that BLU 2 should have become more widespread in ruminants in the United States. The fact that this has not occurred during the past 10 yr is discussed.