Bluetongue, epizootic haemorrhagic disease of deer and related viruses: current situation in Australia.

Since 1975 3 serotypes of bluetongue (BT) virus (BTV) have been identified in Australia: BTV1 (CSIRO156), BTV20 (CSIRO19) and BTV21. At present 2 further BT viruses (DPP90 and DPP192) have been isolated from the blood of healthy cattle in the Northern Territory (NT) and are undergoing identification. There is serological evidence for BTV15 infection in Western Australia (WA) and the NT, and a background level of serological activity to BTV serotypes 1 to 17. In addition, over 50 isolations of epizootic hemorrhagic disease of deer (EHD) viruses (EHDV) have been made and can be divided into 5 main serotypes, CSIRO157, CSIRO439, CSIRO753, CSIRO775 and DPP59. All 5 serotypes occur within the ecological range of Culicoides brevitarsis, however, as for BTV, the high prevalence of antibodies in cattle in the Kimberley region of WA and the top end of the NT suggests other vectors may also be responsible. CSIRO439 has been shown to be closely related serologically to Ibaraki virus while the other EHD viruses were distinct from Ibaraki and from each other. The complex serological relationships between BTV, EHDV and Palyam virus groups are currently being examined using serological and biochemical techniques. It is often difficult to determine the differences between BTV and EHDV serogroup members. Antibodies to both BTV and EHDV have been found in cattle, buffaloes and deer but there has been no evidence of clinical disease in any of these species or in sheep under field conditions in Australia.