Purpura hemorrhagica is an inflamation of the blood vesssel (vasculitis) There seem to be two prerequisites for the development of purpura hemorrhagica: a large amount of antigenic material and an exaggerated immune response.
Most cases of purpura hemorrhagica are associated with previous bouts of strangles.
Unlike strangles, purpura is not infective; horses cannot catch purpura from other horses. Cases of purpura have been reported to be associated with other upper respiratory tract bacterial and viral infections.
In cases of purpura, the immune system damages vessel walls, causing them to become leaky. Blood components leak into the tissues, resulting in swelling. The head, legs and underbelly of the horse are most often affected.
Hemorrhage into the tissues may occur and may be visible as areas of red spotting on the gums and other mucous membranes. Serum may begin to seep from the skin and, in severe cases, the skin may die and slough off, exposing the tissues beneath. Purpura is not limited to the skin. The effects extend to wherever blood vessels run, including the lungs, muscles and the kidneys. This body wide involvement can lead to other clinical signs such as lameness, laminitis, colic, weight loss, and neurologic signs.
Treatment of purpura hemorrhagica is threefold:
- Removal of the antigenic stimulus
- Reduction of the immune response
- Supportive care
This involves dampening the immune response and removing the inciting cause. Horses are usually started on dexamethasone, a corticosteroid, which works to suppress the immune reaction. In addition, the horses are often put on antibiotics to eliminate any underlying respiratory infections and to prevent further infections while they are undergoing immunosuppressive treatment.
Purura hemorrhagica is difficult to predict and prevent. If a horse has experienced a reaction to the strangles vaccine, a veterinarian may recommend the horse not be administered that vaccine again.
Eradication of antigenic stimuli requires drainage of abscesses and exploration of wounds. An endoscopy of the guttural pouches is also important, and flushing should be repeated as many times as needed.