Duration of bluetongue viraemia and serological responses in experimentally infected European breeds of sheep and goats.

The duration of viraemia and the serological responses were studied in two breeds of sheep and two breeds of goats, experimentally infected with bluetongue (BT) virus serotype 4. Viraemia, detectable by cell culture and embryonated chicken egg inoculation, lasted from the third to sixth day until the 27th-54th day post infection (p.i.). Significant differences between sheep and goats were not recorded. Lesbos sheep and goats together appeared to have significantly longer viraemias (n = 9, mean 41.3 days) than east-Friesian sheep and Saanen goats (n = 10, mean 30.4 days, p = 0.0039). Serological response was studied by competitive ELISA (c-ELISA) and agar gel immunodiffusion (AGID) tests. The c-ELISA was more sensitive in detecting BT virus antibodies in all animals than the AGID tests. No significant differences were observed between sheep and goats or between breeds. The epidemiological significance of subclinical infection and the extended BT virus viraemias in Lesbos sheep and goats, in relation to the maintenance of the virus and to overwintering is discussed.