The occurrence of antibody to bluetongue virus in New South Wales. II. Coastal region and age distribution surveys.

Three surveys of cattle for bluetongue (BLU) antibody were conducted over the years 1978-1980 in coastal areas of New South Wales. In each survey the samples were identified by age. The prevalence of BLU-group antibody, demonstrated in a gel diffusion precipitin test, was highest in the north and decreased progressively to the south. Antibody prevalence increased with age. However, according to variations in prevalence by age and region, it was concluded that the activity of relevant viruses was highly variable between years and was geographically discontinuous. Evidence is presented that much of the antibody found, especially in animals less than 4 years old, failed to persist from one year to another. Factors likely to contribute to more persistent reactions in older animals are discussed. Neutralizing antibodies to bluetongue virus serotypes 1 and 21 were demonstrated and prevalence of these was associated with location and age, as was that of group-specific antibody.