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What is Purpura Hemorrhagica?

Strangles, a common cause of purpura hemorrhagica, is an upper respiratory disease caused by an infection of the Streptococcus equi bacteria. This highly infectious condition causes fever, runny nose or eyes, and swelling of the lymph nodes in the jaw or throat areas so severe as to cause difficulties in swallowing and breathing. Purpura hemorrhagica can develop as the bacteria moves to other body systems. While strangles is highly contagious, purpura hemorrhagica is not, and affected horses cannot infect healthy horses.

Purpura hemorrhagica is an immune mediated condition caused by vasculitis, or an inflammation of the blood vessels. This causes bleeding and swelling and is believed to be an allergic reaction to a previous infection of any streptococcal bacteria, such as strangles, or a virus. The resultant swelling can be a source of discomfort and lameness for your horse and needs immediate medical attention to prevent such serious complications as bowel hemorrhages, renal failures, and death.

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Symptoms of Purpura Hemorrhagica in Horses

Signs begin with skin complaints and swelling in various body areas from the inflamed blood vessels, but can rapidly progress to organ failures and death as the condition spreads to wherever the blood vessels travel. You may not see any signs of the condition until 2 to 3 weeks after infection. Symptoms include:

  • Severe vasculitis
  • Red spotting on gums and mucous membranes
  • Oozing serum on skin
  • Skin cells slough off, exposing tissues underneath
  • Swelling in head, belly, chest, and abdomen
  • Swelling in legs
  • Tender and sore legs
  • Extreme soreness
  • Reluctance to move
  • Stiffness
  • Lameness
  • Laminitis
  • Depression
  • Fever
  • Colic 
  • Weight loss
  • Neurologic signs
  • Abscesses 
  • Respiratory distress
  • Bowel hemorrhage
  • Pneumonia
  • Cardiac arrhythmias
  • Renal failure
  • Gastrointestinal disorders
  • Death

Causes of Purpura Hemorrhagica in Horses

Purpura hemorrhagica is believed to be an immune response to a previous infection, which causes the overproduction of antibodies that deposit onto the walls of blood vessels. These blood vessels then hemorrhage into surrounding tissues, which causes various swelling and other symptoms seen. Causes that can trigger this particular immune response include:

  • Streptococcus equi infection, (strangles) 
  • Respiratory tract infection, often from other strains of streptococcal bacteria
  • Viral infection
  • Vaccination against Streptococcus equi

Diagnosis of Purpura Hemorrhagica in Horses

A diagnosis is based on clinical signs, a history of a prior exposure to strangles or other bacterial or viral infections, a physical examination, and the results of testing. Blood tests can show the presence of Streptococcus equi antibodies. Skin biopsies can reveal signs of vasculitis. Other tests include a CBC and serum analysis.

Treatment of Purpura Hemorrhagica in Horses

Treatment aims to reduce the immune system response while removing the cause that triggered it. Corticosteroids are prescribed to reduce inflammation and suppress the immune response. Antibiotics are also given to eliminate the causing infection, as well as to protect your horse against new infections while the immune system is compromised. Antibiotic therapy is often targeted against the strangles bacteria and can last for 2 to 4 weeks.

Other supportive care includes cold water hosing, hydrotherapy, support wraps and bandaging, NSAIDS, drainage of any abscesses, and the administration of gastroprotectants and intravenous fluids. Hand walking and paddock turnout can help to reduce swelling. More severe cases of purpura hemorrhagica may need many more weeks of therapy.

Recovery of Purpura Hemorrhagica in Horses

Recovery of your horse can vary, depending on the severity of the condition. Mild cases with rapid treatment can have a good prognosis. More severe cases may be fatal, or require euthanization. The presence of leg swelling can prolong recovery and cause permanent musculoskeletal damage. Timely treatment is necessary for the recovery of your horse.

Your horse is at a higher risk for purpura hemorrhagica if he has had or been exposed to the strangles bacteria, or was vaccinated against strangles while his antibody levels were high. Talk with your veterinarian about the possibility of your horse developing this condition, especially after a previous strangles infection.

Prevent most cases of purpura hemorrhagica by reducing your horse’s exposure to the strangles bacteria. This can be achieved through biosecurity measures such as:

  • Avoid transporting your horse to known areas of infection
  • Isolate new horses for at least 2 weeks from the rest of the population
  • Isolate infected horses from healthy ones
  • Identify infected or carrier horses through sample testing
  • Create protocols for keeping stalls, aisles, equipment, clothing, tack, and hands infection free