Epidemiology of bluetongue in Australia: the vertebrate hosts

Ruminants became established in Australia after European settlement which commenced in the late 18th century. Bluetongue (BT) disease has never been suspected in cattle or sheep in this country. The species of ruminants found to have antibodies to BT and epizootic haemorrhagic disease (EHD) viruses are cattle, buffaloes, deer, goats and sheep. No antibodies have been found in pigs, horses, marsupials (kangaroos and wallabies) or humans, even in areas of high prevalence of BT and EHD infection. The serological and historical evidence suggests that Indonesia, where ruminants have been indigenous for a very long period, is a more likely source of infection for the Australian BT and EHD viruses than Papua-New Guinea though the method of their entry to Australia is unknown. It is unlikely that all the BT viruses entered from there in ruminants as there has been no importation of ruminants from Indonesia this century. Antibody surveys of cattle have shown that 2 of the 5 Australian BTV serotypes, DPP90 and DPP192 (Gard GP: unpublished data), are restricted to a limited area of the northern part of the Northern Territory of Australia, 1 (serotype 20) to the north of the 18th parallel of south latitude and the remaining 2 (serotypes 1, 21) to the north of the southern limit of the distribution of the suspected vector Culicoides brevitarsis. The prevalence of antibodies to BT and EHD viruses is highest in the far north of the Australian continent and declines rapidly in the middle 3rd. In the southern 3rd, the cattle and sheep are free of BT and EHD antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)