Onchocerca cervicalis: an underestimated cause of equine skin disease?

Onchocerca cervicalis (equine neck threadworm) is a Culicoides midge-transmitted filarial nematode which, like other vector-transmitted diseases, may present an increasing threat to the UK equine population. The clinical syndrome, equine onchocerciasis, most commonly presents as a type of dermatitis and acts as differential diagnosis for several common equine skin conditions including insect bite hypersensitivity, lice infestations, contact dermatitis and pyodermas. O. cervicalis is currently presumed rare and of minor importance in the UK, as equine onchocerciasis is controlled by routine administration of macrocyclic lactones. As the use of these products declines, the incidence of equine onchocerciasis in the UK may increase. There is a lack of research on O. cervicalis in British horses, with the last notable study being published 50 years ago. Recent survey work has highlighted the requirement to increase knowledge and consideration of O. cervicalis in the UK veterinary profession, particularly as a potential cause of skin disease.