Vasculitis Concerns

Q:My filly had a snotty nose and a cough this winter, but she never really got sick--she just looked bad for two to three weeks. Last week, however, all four of her legs became swollen and we discovered a lump on her head. Not knowing what had happened, I hosed her legs down, gave her Bute (phenylbutazone), and put her in a stall for the night. The next morning she was more swollen so I once again hosed her legs, gave her more Bute, but this time I left her loose to move about the yard thinking she must have stocked up due to confinement.

But after a few hours things seemed to get even worse, so I took her to the vet. The veterinarian said she had vasculitis, and he started her on steroids and a couple other drugs, hosed and wrapped her legs, and things appear to be heading the right direction with the swelling reduced.

What I want to know is if we get through this episode, can it recur for the rest of her life, or is it now cured? This seems like a serious condition that could make her unable to pasture if not watched daily to catch recurrences. Please tell me if it's worth putting more time and training into an animal with this condition.

Kim Grant, via e-mail

A:Vasculitis is a term that describes inflammation of the walls of blood vessels. It can be caused by a variety of different conditions, but it is usually precipitated by a reaction of the horse's own immune system against bacteria, viruses, rickettsial organisms (such as the one that causes Potomac horse fever), drugs and medications, or for unknown reasons.

Based on the filly's history of recent respiratory disease, one of the more likely explanations for vasculitis in your horse would be purpura hemorrhagica, which is associated with exposure to Streptococcus equi ssp. equi (the bacteria that cause strangles), or less commonly, equine influenza. Most horses with strangles or influenza recover uneventfully. However, some horses develop complications including purpura hemorrhagica, where antibodies combine with the bacteria or virus and are deposited in the walls of the blood vessels, leading to inflammation and leakage of fluid. This causes pain and edema (fluid swelling) similar to what you describe in your horse.

The most accurate way for your veterinarian to diagnose vasculitis (including purpura hemorrhagica) is by biopsy, where a small skin sample is examined under a microscope. In this case, however, I would probably start with a simple blood test, the Strep M-protein ELISA (SeM), to look for evidence that your horse has had recent strong exposure to the strangles bacterium. A high SeM titer would be strongly suggestive of purpura hemorrhagica.

Was your horse vaccinated for strangles shortly before these signs occurred? Vaccination can occasionally trigger purpura hemorrhagica in horses that have been previously exposed. Also, if your filly hasn't had a Coggins test this year, this should also be performed to rule out equine infectious anemia. Other causes to eliminate are drug reactions: If your mare was receiving any medications (even herbal or over-the-counter drugs) for her illness over the winter, speak to your veterinarian about discontinuing them if you have not already done so.

Treatment of vasculitis usually involves suppressing the immune system and reducing inflammation with quite high doses of corticosteroids; these usually need to be administered for at least two to four weeks to prevent relapse when they are discontinued. Most veterinarians also add penicillin or a similar antibiotic if they suspect the vasculitis is caused by Strep bacteria. The chance of full recovery from vasculitis depends on its cause, but most horses with purpura hemorrhagica survive and have no further complications. Relapse can occur if the corticosteroids are stopped too early, but this usually happens within a week or two of discontinuing treatment; if your filly is fine after this point, I'd stop worrying and just treat her like a normal horse.

About the Author

Rose Nolen-Walston, DVM, Dipl. ACVIM

Rose Nolen-Walston, DVM, Dipl. ACVIM, is an assistant professor of large animal internal medicine at the University of Pennsylvania School of Veterinary Medicine’s (Penn Vet) New Bolton Center, in Kennett Square. She graduated from the University of Georgia College of Veterinary Medicine in 2001, and then completed an internship and residency in large-animal internal medicine at Tufts University, in North Grafton, Massachusetts. She spent a subsequent year at Tufts doing research in adult stem-cell biology in mice. She joined the Penn Vet faculty in 2007, where she won the university’s 2013-2014 Lindback Award for Distinguished Teaching.

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