The interval after infection when bluetongue virus (BTV) was present in the blood of calves inoculated with BTV serotype 10 (BTV 10) was evaluated by virus isolation (VI) in embryonated chicken eggs (ECE), BTV-specific polymerase chain reaction (PCR), and in vitro blood feeding of vector Culicoides variipennis (C.v.) sonorensis. BTV nucleic acid was detected by PCR in blood cells for 16 to 20 weeks after infection whereas infectious virus was detected by VI in ECE for 2 to 8 weeks. BTV was detected in calf blood by in vitro feeding of C.v. sonorensis for only 0 to 2 weeks after inoculation of calves with BTV 10. Selected bloods which were positive by PCR analysis but not by VI in ECE were not infectious for sheep. The data are consistent with the hypothesis that prolonged viremia in BTV-infected cattle results from association of the virus with blood cells, especially erythrocytes. The fact that calf blood that contained viral nucleic acid as determined by PCR analysis, but not infectious virus as determined by VI in ECE, was not infectious for either the insect vector or sheep suggests that cattle whose blood contains BTV nucleic acid but not infectious virus are unimportant to the epidemiology of BTV infection.

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Vesicular stomatitis virus serotype New Jersey (VSNJV) was mixed with bovine blood or fetal bovine serum (FBS) and fed across silicone membranes to laboratory populations of Culicoides sonorensis Wirth & Jones. In an initial study, virus was detected after 13 d in 21% of the midges that received an FBS/VSNJV mixture. In subsequent time-course experiments, engorged females were collected and maintained at 20.0 degrees C and assayed for VSNJV immediately after feeding and at 1, 3, 7, 10 and 13 d after feeding. Virus was detected after 13 d in 3% of the midges that received a bovine blood/VSNJV mixture and in 9% of the midges that received an FBS/VSNJV mixture. The results indicate that C. sonorensis should be considered as a potential biological vector of VSNJV.