Isolation and propagation of bluetongue virus in embryonating chicken eggs

The incidence of bluetongue (BT) disease in sheep in Israel during 1964-1982 was presented. The intravenous (IV) and the yolk-sac (YS) routes of inoculating embryonating chicken eggs (ECE) for primary isolation and propagation of BT virus (BTV) were compared and assessed. It was shown that the IV route of inoculation was about 100- to 1,000-fold more sensitive than the YS route; also, by the IV route, virus isolation was more rapid and assays were more clear cut. About 30% of virus isolations from field samples obtained by the IV route were missed when the YS route was used. Ten to 13-day-old ECE were equally susceptible to replication of BTV. The growth characteristics in ECE were different for BTV serotypes 2, 4, 6, 10 and 16. Titratable virus replication preceded ECE mortality by 1 or 2 days. The maximum viral titre in live ECE was usually lower than the maximum titre in dead ECE. BTV serotypes 2, 4, 6 and 16 were isolated from Culicoides imicola in IV inoculated ECE.