Distribution of bluetongue and other arboviruses in northern Australia

Abstract

A serological survey of cattle from throughout Queensland and sheep from cattle/sheep interface areas was conducted to determine the distribution and prevalence of antibodies to Bluetongue virus serotypes. This information allowed preliminary designation of arbovirus-free zones and identification of livestock populations at greatest risk to introduction of exotic Bluetongue viruses.
Throughout the state antibodies were detected to only serotypes 1 and 21. In cattle, prevalence decreased with increasing distance from the coast ranging from 73 % in the far north to less than 1 % in the southwest.
In sheep, prevalence of bluetongue antibodies in the major cattle/sheep interface areas in the north-west and central Queensland ranged from 0% to 5%.
A system of strategically placed sentinel herds of 10 young serologically negative cattle was established across northern Australia to monitor the distribution and seasonality of bluetongue viruses. Initially 23 herds were located in Queensland, 4 in Northern Territory and 2 in Western Australia but by the completion of the project the number of herds in Queensland had been reduced to 12.
No bluetongue virus activity was detected in Western Australia or Northern Territory herds throughout the project although testing of one herd in Northern Territory with a history of bluetongue activity was not done after June 1991.
In Queensland, activity to bluetongue serotypes 1 and 21 was detected in all years of the project. Transmissions occurred predominantly in the period April to September and were more widespread in wetter years.
The pathogenic bluetongue serotypes previously isolated from the Northern Territory have not spread to adjoining States.