Abstract
Climate and environmental data were used to estimate the risk of testing positive for antibodies to bluetongue (BTV) and epizootic hemorrhagic disease viruses (EHDV) in cattle in Illinois and western Indiana over three transmission seasons (2000-2002). The risks of BTV and EHDV seropositivity were positively associated with temperature during every year of the study. The EHDV seropositivity was also positively associated with forest patchiness in two of the years. During 2002, a year with unusually high spring rainfall, forest patchiness was not significantly associated with EHDV but spring rainfall did have a moderating effect on temperature. Maps of predicted probability of exposure to BTV or EHDV were created using these best-fitting models and show distinctly different spatial patterns within the same cattle population.