Equine bullous pemphigoid (EBP) is an IgG-mediated autoimmune blistering disease targeting the hemidesmosomal proteins bullous pemphigoid antigens 1 and 2. It is characterized by the development of large, tense blisters in the skin of the horse's face. It occurs somewhat rarely in horses, but is the most common subtype of autoimmune blistering disease in humans. EBP is caused by immunologic attack of the basement membrane zone by autoantibodies. It is suspected to be triggered by stress, neoplastic disease or other infections.
Early clinical signs include the development of crusting lesions around the horse's eyes. Over time, these lesions will turn into sub-epidermal vesicles and erosions that spread to other areas of the face--the mouth, nose, tongue and vulva. Horses with advanced stages of the disease often produce ulceration with epidermal collarettes and crusting. Many horses become depressed and lose their condition parallel to loss in appetite, fever and weight loss.