Purpura is an immune-mediated attack on the blood vessels. This causes what is called "vasculitis" - inflammation of vessels. Damaged blood vessels allow the fluid part of the blood (plasma or serum) to ooze through the vessel wall and collect as edema in the tissue planes. Purpura usually occurs weeks after recovery from infectious respiratory diseases, usually Strangles and other Strep infections, but sometimes after respiratory viruses like Influenza or Rhinopneumonitis. In rare cases, it can follow Strangles vaccination.

This condition is rare and sporadic. It does not affect the majority of horses that have had respiratory disease, only a small percentage.

This is a severe and painful condition. Damaged blood vessels ooze fluid through their walls, allowing the collection of fluid in the connective tissues of the legs and other areas. The signs of this condition include painful, warm swelling (mostly of the legs), fever, depression, and loss of appetite.

Sometimes swelling also develops on the belly or muzzle. In some cases, swollen areas can ooze blood or amber colored serum. The gums often have red spots or blotches caused by ruptured blood vessels. Edema (fluid accumulation) within the tissues of the respiratory tract can cause labored breathing.

Diagnosis requires rule out of similar appearing diseases and usually follows a history of respiratory disease.

Treatment usually requires steroids and supportive nursing care.