BLUETONGUE VIRUS AND THE SOUTHERN OSCILLATION INDEX - EVIDENCE OF AN ASSOCIATION

Bluetongue virus serological-testing results from a sentinel-herd sche me in Queensland, Australia were analysed for seasonal trends using ti me-series analysis. Between 1990 and 1994, 116 cases of seroconversion to bluetongue viruses were detected. Cases occurred mostly in autumn and the median month of seroconversion was May. No significant (P=0.95 ) linear trend was detected in the time-series. The association betwee n the southern oscillation index (SOI, an index based on air pressure differences between the Pacific and Indian Oceans which has been linke d to periods of drought in northern Australia) and cases of seroconver sion to bluetongue viruses were examined, More cases occurred during m onths in which the SOI was positive, compared with months in which it was negative (P=0.04). Monthly incidence of seroconversion per 100 cat tle at-risk was best described by: log(incidence(t))=0.46+/-0.36 log(i ncidence(t-1))+0.015 SOIt-1.