Impact of climate change on the occurrence and distribution of bluetongue in Europe

Climate changes may have significant impact on animal health, including changes in the distribution and seasonality of vector-borne diseases. Arboviruses, such as bluetongue virus (BTV), are particularly susceptible to climate change because of their small size and their ability to adapt to variations in the temperature of the environment. Climate also has long-term indirect effects on the transmission of BT via its effects on the distribution and availability of suitable habitats. Changes in BT incidence in Europe have been matched by spatio-temporal changes in regional climates, including the specific climatic drivers of BTV infection. The climate changes are responsible for the occurrence and distribution of BT through their impact on the viral vectors. Changes in climate, i.e. temperature, precipitation, humidity, wind, etc., can influence various aspects of the Culicoides vectors' life cycle, including survival, population numbers, vector-pathogen interactions, pathogen replication, vector behaviour and, of course, its distribution. Different species of Culicoides have different environmental tolerances, and the optimal temperature and humidity levels for populations of Afro-Asiatic species, such as C. imicola, are different from those for Palearctic species, such as the C. obsoletus and C. pulicaris groups. However, the biotic processes of changing vector roles and distribution have been as important as the climatic process in driving the invasion of Europe by multiple BTV strains. The enhanced transmission of BTV by indigenous European vectors has been instrumental in the spread and persistence of infection in cooler and wetter areas of different regions of Europe after the invasion. The vectorial capacity of Culicoides is dynamic and climate-mediated, making it difficult to state unequivocally that particular species cannot or will not be involved in transmission-even of strains that enter Europe unexpectedly from geographically remote regions.