PHYLOGENETIC CHARACTERIZATION OF BLUETONGUE VIRUSES FROM NATURALLY-INFECTED INSECTS, CATTLE AND SHEEP IN AUSTRALIA

The polymerase chain reaction was used to detect the presence of blue- tongue virus (BTV) in a number of clinical and insect samples collecte d in the Northern Territory of Australia. Sequence analyses of the amp lified BTV genes differentiated endemic Australian and exotic viruses. Two potential exotic BTV were detected as a result of PCR analyses of blood from sentinel animals and of the insect vector, Culicoides wada i. The detection of BTV in C wadai was the first direct demonstration of the presence of BTV in this potential vector. This new technology c an significantly reduce the time taken for a diagnosis from a clinical sample and increase the amount of useful information obtained on a BT V isolate by using rapid sequencing techniques. Sequence data were use d to differentiate between BTV20 isolated in 1975 and two isolates of the same serotype, isolated in 1992, and indicated that the latter wer e probably a recent incursion into Australia from Indonesia due to the ir greater VP3 sequence homology to the BTV9 (Java) than to Australian BTV isolates.