Infection of cattle in Queensland with bluetongue viruses: II. Distribution of antibodies

Abstract

A survey of the distribution of serum antibodies to bluetongue viruses in Queensland cattle herds was conducted in 1989. A total of 410 herds were selected in which sera from 20 or more cattle had been tested with the agar gel immunodiffusion (AGID) test. Estimates of prevalence were standardised for age of cattle and adjusted using results from serum neutralisation (SN) tests. Spatial statistical methods were used to investigate the distribution of these selected herds with respect to the prevalence of serum antibodies to bluetongue viruses. The mean herd prevalence was 5.2% (95% confidence interval 4.5 to 5.9) and the median herd prevalence was 3.5% (95% CI 2.8 to 4.2). Prevalence was highest in far north Queensland (17.3%) and lowest in south-west Queensland (0.3%). Significant (P < 0.01) clustering of selected herds with respect to prevalence of serum antibodies was found. Herds with prevalence of serum antibodies to bluetongue viruses above the overall mean herd prevalence were significantly (P < 0.05) clustered in the north-west, far north and northern and southern coastal regions of Queensland. Clustering within the north-west and southern coastal regions of Queensland was more pronounced than the clustering detected in the northern coastal and far north regions.