Investigating and Treating Sweet Itch in horses*

Investigating and Treating Sweet Itch in horses

Sweet Itch is an equine hypersensitivity reaction to the biting insect Culicoides. The immune response is directed against salivary proteins of midges of this genus, and affected individuals often show positive for IgE antibodies against other biting insects including Simulium. It is the most common allergic skin disease of horses and there is a strong hereditary component with certain breeds being overrepresented (Welsh, Shire and Icelandic breeds). A seasonal pruritus of the predilection sites (mane, tail base, dorsal and ventral midline) is the main clinical sign leading to self inflicted trauma from excoriation, affected individuals usually developing the disease from 4-5 years of age and become progressively worse as they get older. The constant skin irritation gives rise to alopecia, ulceration, erosion, excoriation and lichenifi cation of affected areas of skin, and the restlessness can interfere with grazing and result in weight loss. Investigation of Sweet Itch in horses using serology and intradermal skin testing (IDT) has been well documented and different treatment approaches including allergen-specifi c immunotherapy (ASIT) have been tried. This article describes the approach to diagnosing this skin disease in the horse and the various treatment options are illustrated.