Large Strongyle S. vulgaris Still a Risk for U.S. Horses

While largely considered eradicated in domestic horses, researchers found that most feral horses tested positive for the internal parasite.
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Large Strongyle S. vulgaris Still a Risk for U.S. Horses
Owners should quarantine new horses, particularly feral ones, to their properties and treat them for large strongyles before letting them commingle with resident horses. | Photo: iStock
When thinking of internal parasites in horses, many of us quickly produce images of small strongyles or cyathostomins in our heads. This is understandable considering small strongyles are now the most common parasites in horses. That said, Strongylus vulgaris, the most pathogenic (disease-causing) of the large strongyles, shouldn’t stray too far from our thoughts.

S. vulgaris remains one the most dangerous parasites for horses because the migrating larvae can cause blood clots and damage to arteries leading to the abdomen, which, in turn, could result in colic,” says Jennifer Cain, MS, a PhD student and graduate research assistant in the University of Kentucky’s Department of Veterinary Science. “While S. vulgaris has largely been eliminated in domestic horse populations thanks to the power of ivermectin, unmanaged populations, including wild and feral horses, are still burdened by these parasites. When captured and adopted out, wild horses can serve as a reservoir for S. vulgaris.

Cain reminded horse owners that with growing parasite resistance to deworming agents and no effective alternatives, exposing unmanaged horses to S. vulgaris poses potential risk.

To demonstrate the science surrounding this concern, Cain and co-workers collected fecal samples from 28 feral horses in Louisiana and 10 domestic horses living on nearby equine operations. They then performed fecal egg counts (FECs) and testing for S. vulgaris using a DNA-based analyses on samples from the horses. The researchers strategically dewormed the domestic horses—only those with FECs >200 eggs/gram of feces received a chemical dewormer as recommended by the American Association of Equine Practitioners

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Written by:

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she’s worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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