INFECTION OF CATTLE IN QUEENSLAND WITH BLUETONGUE VIRUSES .2. DISTRIBUTION OF ANTIBODIES

A survey of the distribution of serum antibodies to bluetongue viruses in Queensland cattle herds was conducted in 1989. A total of 410 herd s were selected in which sera from 20 or more cattle had been tested w ith the agar gel immunodiffusion (AGID) test. Estimates of prevalence were standardised for age of cattle and adjusted using results from se rum neutralisation (SN) tests. Spatial statistical methods were used t o investigate the distribution of these selected herds with respect to the prevalence of serum antibodies to bluetongue viruses, The mean he rd prevalence was 5.2% (95% confidence interval 4.5 to 5.9) and the me dian herd prevalence was 3.5% (95% CI 2.8 to 4.2). Prevalence was high est in far north Queensland (17.3%) and lowest in south-west Queenslan d (0.3%), Significant (P < 0.01) clustering of selected herds with res pect to prevalence of serum antibodies was found. Herds with prevalenc e of serum antibodies to bluetongue viruses above the overall mean her d prevalence were significantly (P < 0.05) clustered in the north-west , far north and northern and southern coastal regions of Queensland. C lustering within the north-west and southern coastal regions of Queens land was more pronounced than the clustering detected in the northern coastal and far north regions.