Insect Bite Hypersensitivity in Horses: Causes, Diagnosis, Scoring and New Therapies

SIMPLE SUMMARY: Insect Bite Hypersensitivity (IBH) is the most common cause of itchiness in horses and occurs when individual horses are allergic to the bites of midges or other insects. The itchiness leads to rubbing and often traumatic injury to the skin. There is currently no cure for this disease and management is life-long and costly. This review describes the causes, immune effects, diagnosis, and severity grading as well as traditional treatment and management strategies. Newer treatments for this disease, including topical treatments and vaccination, are also presented. ABSTRACT: Insect Bite Hypersensitivity (IBH, Queensland itch, sweet itch, equine summer eczema) is the most common pruritic disease of horses. It is most often caused by sensitivity to the saliva of Culicoides spp. of biting midges; however, it can also be caused by hypersensitivity to other insect species. The prevalence of IBH in horses is reported to be as high as 60% in some parts of the world. Due to the severe pruritus and effects of secondary self-trauma, IBH has animal welfare concerns, and there is currently no cure. Management of this condition is life-long, time consuming and costly. New grading systems to document disease severity are being validated, which will allow the comparison of clinical trial results of new and existing therapies. Management involves the minimisation of insect bites by use of stabling, fans, rugs and repellents. Symptomatic therapy involves the administration of systemic or topical corticosteroids, systemic antihistamines, and creams and sprays to promote skin healing and decrease inflammation. New immune-mediated therapeutics including vaccines, in addition to desensitisation procedures, show promise at controlling hypersensitivity reactions. This article will review aetiologic agents, pathophysiology, scoring systems and current and new therapies.