Bluetongue surveillance methods in an endemic area: Australia

Surveillance for bluetongue (BT) viruses (BTV) has been carried out in the Northern Territory, Australia since 1980. The number of sites, intensity of sampling and methods of testing have varied during this period. Monthly serology is conducted at a number of sentinel sites and intensive weekly sampling for virus isolation is conducted at the site of highest known arboviral activity. This has enabled the isolation of all eight BTV serotypes identified in Australia. Natural viraemias are between one and eight weeks. No additional serotypes have been isolated since 1986. However, genetic analysis of isolates has shown incursions of viruses of South-East Asian origin in 1992, 1994 and 1995. Trapping for Culicoides spp. has also been carried out at these sites on a regular basis. In recent years, an annual serological survey has supplemented the sentinel herds to more accurately define the BT zones described under OIE guidelines.