Bluetongue Incidence in Southern Portugal is Determined by Climate

Species distributions are constrained at wider spatial scales by the suitability of climatic conditions. Shifting climates will cause species to shift their distributions, so to track shifting climatic suitability. The spread of infectious diseases depends upon the species' presence in their transmission cycle, such as vectors, reservoirs and hosts. It follows that similarly to species distributions, the incidence of some infectious diseases, including viruses and bacteria, will be altered accordingly. Being able to predict the spatial and temporal occurrence of diseases is important in preventing and/or managing future disease incidences. We evaluated the effect of vector climatic suitability and wind direction on bluetongue outbreaks in Alentejo, Southern Portugal. This is relevant because the disease has an important economic impact on livestock production. We concluded that the suitability of the disease’s main vector, Cuclicoides imicola, a tropical and subtropical species, is one of the best predictors of the spatial occurrence of disease outbreaks from 2004 to 2021, with a less relevant role being played by Cuclicoides dewulfi, a European species. Wind direction also had a significant but residual effect on outbreak occurrence. These results highlight the relevance of understanding the factors driving vector presence and suitability in order to be able to plan ahead and mitigate the impacts of infectious diseases. In the case of diseases affecting species of economic relevance, these impacts are not only measured in terms of mortality but also economically.