CLIMATIC FACTORS ASSOCIATED WITH THE INFECTION OF HERDS OF CATTLE WITH BLUETONGUE VIRUSES

The incidence of bluetongue virus infection of 15 cable herds in Queen sland, Australia, was determined by a serum neutralization test. The m aximum temperature (degrees C), minimum temperature (degrees C) and ra infall (mm) data were obtained from the meteorological recording stati ons closest to each herd. Using unweighted least-squares regression an alysis, the best statistical model explaining the most variability in the herd incidence rate included the ratio between the maximum and min imum temperature recorded at both 1 month and 6 months preceding seroc onversion, and rainfall recorded at both 2 months and 6 months precedi ng seroconversion. More than 90% of the variability in the incidence o f bluetongue virus infection in the herds was explained by the model, a considerable improvement on previous models that used prevalence dat a. The prospective nature of the study also supports a strong causal r elationship between climatic factors and the occurrence of infection i n cattle herds.