Local investigation into the role of Culicoides species diversity (Diptera: Ceratopogonidae) in recurrent horse dermatitis cases in southwest France

Background. Insect bite hypersensitivity in horses (“sweet itch”) is the most common pruritic, chronic, seasonal, and recurrent dermatitis resulting from an allergic reaction in horses to the saliva of Diptera: Nematocera, primarily from the Culicoides genus. This dermatitis affects 10% of horses in France and is a major concern for the horse industry and private owners. Given the frequent occurrence of this health problem and the limited investigation in France, we conducted a field survey in the vicinity of a riding stable in south-western France with a reported chronic case of recurrent horse dermatitis to (i) characterize the Culicoides species associated with horse populations (hippophilic species) and (ii) estimate the relative abundance of the different species identified based on the trapping site location. Methods. For this purpose, three OVI traps were set up for one night once a week, from mid-June to the end of July 2022, the known peak activity period. Traps were placed either indoors or outdoors at horse facilities. Results. Twelve species were morphologically identified. Culicoides obsoletus and C. scoticus were predominant at all trapping sites. Culicoides circumscriptus and C. nubeculosus were the second most common species found, followed by C. punctatus , C. festivipennis , and C. pulicaris . Importantly, certain species ( C. obsoletus / C. scoticus and C. circumscriptus ) were found in significant quantities indoors. Conclusions. The presence of these insects indoors in substantial numbers raises questions about the main prevention recommendation, which advises stabling horses from the end of the afternoon until the next morning.