Seasonality of infection of cattle with bluetongue viruses

Abstract

A Cox proportional hazards model with time-dependent covariates describing the risk of serocon-version of cattle to bluetongue viruses, as a function of climatic variables (maximum temperature, minimum temperature and rainfall), was used to investigate the seasonality and geographical distribution of bluetongue virus infection in Queensland, Australia. Cases of seroconversion in Queensland (which mostly occur in autumn and winter) were associated with summer and autumn temperature and rainfall at all but one of the 50 locations studied. In far north Queensland, most cases of seroconversion were associated with temperature and rainfall in the summer months, whereas in the remainder of Queensland most cases of seroconversion were associated with autumn temperature and rainfall. Thus, simulation results suggest that two ecological cycles of bluetongue virus infection of cattle exist, and may support a hypothesis of differential transmission by vector species in Queensland.