Assessing infection rates in field‐collected <i>Culicoides</i> populations: Example of a large‐scale study on bluetongue and epizootic hemorrhagic disease viruses in <i>Culicoides</i> species (Diptera: Ceratopogonidae) in Reunion Island, Indian ocean

Characterising the vector role of a species is critical to understand and quantify host-vector-pathogen interactions. This role has to be assessed for each suspected vector species, but also at the population level. Indeed, different populations of the same species can exhibit biological and ecological variability that can amplify or limit their epidemiological role in transmitting pathogens to human and/or animal populations. In this work, we characterise the spatio-temporal dynamics of two major viruses of veterinary interest (bluetongue virus [BTV] and epizootic hemorrhagic disease virus [EHDV]) in the five species of Culicoides (Diptera: Ceratopogonidae) present in Reunion Island, located in the Indian Ocean. Our aim is to quantify the infection rates of the two viruses in field-collected Culicoides over a 2-year period. A total of 33,358 individuals comprising 11,504 pools were molecularly screened to detect the presence of both viruses. Our work applied an original statistical approach based on the use of Bayesian inference and showed that all five Culicoides species could be involved in the transmission of the two viruses with different levels of infection. EHDV circulated within Culicoides populations for only 4 months over the study period, while BTV circulated within the same populations throughout the entire 2-year period. We hypothesized that although both viruses are transmitted by the same Culicoides species, they exhibit distinct epidemiological patterns: BTV displays enzootic circulation in Reunion Island, whereas EHDV shows an epizootic pattern.