In Australia the major vectors are C. wadai , C. brevitarsis, C. fulvus and C. actoni . Other species of Culicoides have been shown to be less efficient vectors. The efficiency of vector species of Culicoides in transmitting BTV varies, depending on the virus strain and the local sub-population of the insect involved. Viraemia may last for up to 54 days in sheep and goats and for up to 100 days in cattle, though it is usually much shorter in all 3 species. Infected animals develop detectable levels of antibody within four weeks of infection but in many cases antibodies may be detected as early as seven days, which means that a period of concurrent viraemia and antibody may exist for a significant time.
Detectable antibodies persist for longer than the period of viraemia.
For the detection of virus, sheep inoculation, intravenous inoculation of chick embryos and cell cultures are used, in decreasing order of sensitivity. In addition PCR techniques have been developed which are giving promising results. With the AGID, cross reactions with EHDV antibodies are common. For the detection of type-specific antibodies virus neutralisation tests are used. The adoption of International standard reference sera or the carrying out of interlaboratory comparisons is recommended in order to standardise laboratory results.