Risk mapping of bluetongue virus in Montana using habitat suitability for Culicoides vectors

Abstract

Bluetongue disease, first reported in the United States in 1952, affects cattle, sheep, and other wild and domesticated ruminants. Globally, the biting midge (order Diptera, family Ceratopogonidae, genus Culicoides) has been identified as the primary vector for the spread of bluetongue. Preliminary research has demonstrated that outbreaks of arboviruses can be accurately predicted using habitat characteristics essential to vector survival, as global disease occurrence is closely correlated to distribution of the disease vector. The goal of my study was to derive an accurate map ofstatewide habitat suitability for C. sonorensis based on individual environmental factors, which could then be used to infer bluetongue risk. I used the program MaxEnt to build a statewide habitat suitability model for the biting midge, Culicoides sonorensis using environmental data layers and presence-only data for known locations throughout Montana. Modeling with MaxEnt resulted in a statewide map of C. sonorensis habitat with an AUC=0.928, demonstrating a strong correlation between the model and the presence data. Environmental variables incorporated into the final model included distance to surface water, land cover, slope, and elevation. The MaxEnt output of midge habitat suitability shows highly suitable habitat in eastern Montana, which becomes drastically less hospitable in the western part of the state, presumably due to higher elevation, which is known to limit midge distributions. Although this project produced a highly significant model, the low amount of presence data for C. sonorensis resulted in a limited number of training points for modeling analysis, and should be expanded in order to further legitimize the results and allow for use oftest data.