Lower Bird Evenness and Diversity Are Associated With Higher Usutu Prevalence in Culex pipiens Mosquitoes

The mosquito-transmitted Usutu virus has spread in the last few years, becoming endemic in several areas of Europe, such as in the southern French region of the Camargue. Our aim was to study the relationships between the presence of the viral agent in Culex mosquitoes and the structure of bird communities in the context of the dilution effect.

We carried out mosquito and bird censuses in several selected localities across a land-use gradient and screened mosquito pools for flaviviruses. We focused on exploring how host bird diversity, richness, abundance and evenness were associated with Usutu detection in Cx. pipiens.

Usutu virus was detected in seven pools of Cx. pipiens, and phylogenetic analysis identified Usutu lineage Africa 3, confirming its circulation. The probability of detection in mosquitoes is associated with areas with lower bird evenness and diversity but higher bird abundance and richness and higher Cx. pipiens abundances.

Bird evenness was the variable with the greatest explanatory power, being negatively related to the probability of detecting Usutu in Cx. pipiens, supporting a dilution effect. These results will help us better understand the relationships between bird community structure and the risk of Usutu mosquito-borne disease.