Simulation modeling of the effect of climatic factors on bluetongue virus infection in Australian cattle herds. II. Model experimentation

Abstract

Using a state transition model based on matrix formulation, the effect of climatic factors on bluetongue virus infection was investigated in a simulated cattle herd in Queensland, Australia. Changes in spring rainfall had the most influence on predicted prevalence of infection, and changes in seasonal minimum temperature had more effect on predicted prevalence than changes in seasonal maximum temperature. Four medium-term (i.e. 25–30 years) climatic scenarios were simulated: warm, wet spring and autumn seasons, and dry, cool spring and autumn seasons. The predicted prevalence of infection was suppressed approximately four-fold when a series of dry, cool autumn seasons were simulated, compared with the other scenarios. Occurrence of dry, cool autumn seasons at least once every 4 years or less had the greatest effect on predicted prevalence of bluetongue virus infection. Results suggest that drought conditions in Australia may affect the endemic stability of bluetongue virus infection. Instability in the system could lead to cyclical epidemics of infection, may explain previously observed variability in bluetongue virus infection, and might lead to outbreaks of bluetongue disease in commercial sheep flocks in Australia.