Summary
A group of 44 sheep was vaccinated with the bivalent modified-live vaccine against bluetongue virus (BTV) serotype 2 (BTV-2) and BTV-9 to evaluate viraemia and antibody kinetics. Blood samples were taken from the sheep three times a week for two months and screened for the presence of BTV and for antibody using the competitive enzyme-linked immunosorbent assay (c-ELISA) and the virus neutralisation (VN) test. Intravenous egg inoculation, followed by two blind passages in Vero cells, was used to isolate BTV-2 and BTV-9 from the ethylene-diaminetetra-acetic acid (EDTA) blood samples; virus titres were also determined in the viraemic animals. BTV was detected in the blood of 39 sheep between day 3 and day 24 post vaccination (pv). Viraemia peaked on day 7 pv with average titres of 10 ^5.3 TCID ₅₀ /ml. Antibodies were first detected in the c-ELISA on day 6 pv and by day 16, all sheep were seropositive. Only 36 of the 44 inoculated sheep developed virus-neutralising antibodies against both BTV-2 and BTV-9 while 4 were positive to BTV-2 only; neutralising antibodies were not detected in the 4 remaining animals. Antibody titres were very low and unstable and often bordered on the negative/positive threshold.

Keywords
Bluetongue, Competitive enzyme-linked immunosorbent assay, Sheep, Vaccine, Viraemia, Virus, Virus neutralisation.