Allergies are becoming increasingly common in both humans and horses. The most problematic hypersensitivity is the allergy to Culicoides stings, also known as "summer scabies".
Clinical signs :
In Belgium, "summer scabies" manifests itself in horses and donkeys as a pruritic dermatitis affecting mainly the mane and tail area but also the back line. It is characterised by crusty, excoriated lesions with hair loss due to pruritus. Horses may also suffer from atopic dermatitis and/or food allergy with lesions often induced by pruritus. They also have the particularity of rapidly developing urticarial lesions.
In horses and donkeys, the history of dermatitis, symptomatology and seasonality are suggestive. Intradermal or blood tests (serology) are most often unreliable!
For summer scabies, it is advisable to bring horses into the stable before nightfall and only take them out after sunrise, use protective blankets (some contain insecticides) and use repellent insecticides. Antihistamines and glucocorticoids (spray or oral) are sometimes necessary.
Other allergies: atopic dermatitis and food allergy are described but little documented for the horse. Allergies remain, as in humans, complex to identify and treat.