DETECTION OF BLUETONGUE VIRUS IN THE BLOOD OF INOCULATED CALVES - COMPARISON OF VIRUS ISOLATION, PCR ASSAY, AND IN-VITRO FEEDING OF CULICOIDES-VARIIPENNIS

The interval after infection when bluetongue virus (BTV) was present i n the blood of calves inoculated with BTV serotype 10 (BTV 10) was eva luated by virus isolation (VI) in embryonated chicken eggs (ECE), BTV- specific polymerase chain reaction (PCR), and in vitro blood feeding o f vector Culicoides variipennis (C.v.) sonorensis. BTV nucleic acid wa s detected by PCR in blood cells for 16 to 20 weeks after infection wh ereas 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 O to 2 weeks after inoculation of calves with BTV 10. Selected b loods which were positive by PCR analysis but not by VI in ECE were no t infectious for sheep. The data are consistent with the hypothesis th at prolonged viremia in BTV-infected cattle results from association o f the virus with blood cells, especially erythrocytes. The fact that c alf blood that contained viral nucleic acid as determined by PCR analy sis, but not infectious virus as determined by VI in ECE, was not infe ctious for either the insect vector or sheep suggests that cattle whos e blood contains BTV nucleic acid but not infectious virus are unimpor tant to the epidemiology of BTV infection.