Salivary gland homogenates from the vector Culicoides variipennis may aid in detection of bluetongue virus in chronically infected cattle.

Studies were conducted on 2 cows chronically infected with bluetongue virus (BTV) acquired in utero from their dam. In previous research, BTV had been isolated 4 times from 1 cow and 8 times from the other. BTV was undetectable between spontaneous febrile and leukopenic episodes and antibodies to BTV were not detectable in the serum. Previous work had shown that bites by uninfected females of the vector Culicoides variipennis (Coquillett) caused virus to recrudesce in the blood to detectable levels in a bull with a similar BTV infection. After 1 of the 2 cows became hypersensitive to the bites of the vector, the cows were inoculated with homogenized salivary glands from the vector in an effort to increase the viral concentration to detectable levels. Bites by uninfected vectors were used 9.5-48 hr after inoculation of salivary glands in attempts to recover BTV biologically. In 2 of 6 experiments, after inoculations of the glands, BTV was isolated and confirmed from some of the blood samples and from some pools of C. variipennis females that had blood fed on both animals.