Today's EPM

What have we learned about equine protozoal myeloencephalitis (EPM) since it first was reported in 1995? A lot, and not enough. EPM has been called the "most overdiagnosed neurologic disease in the United States" by some researchers and veterinarians, yet we really don't know how many horses are affected each year by this disease. Estimates are that thousands show actual clinical signs that are observed by owners. Some horses have clinical signs so mild that the underlying disease is never discovered. Other horses die from the disease. By 1995 researchers had made some big discoveries about the disease. For example, David Granstrom, DVM, PhD, had developed the first test able to detect the presence of antibodies against the causative single-celled protozoan parasite Sarcocystis neurona while he worked at the University of Kentucky's Gluck Equine Research Center.

The term EPM is still among the top searches performed at, leading us to wonder about the occurrence of this disease. A poll about EPM conducted on indicated that out of 1,328 respondents, 37.8% have owned a horse with EPM, 28.4% have had a friend with an EPM horse, and 26.3% agreed "there have been many cases around me."

Since horses are affected, there is no vaccine, there is no cure, and horse owners are concerned, this month we offer a three-part series on the diagnosis, treatment, and prevention of EPM that includes updated information from industry experts (articles begin on page 30).

You also should read the Across the Fence (page 82) on one horse losing the battle with EPM.

We don’t have all the answers on EPM yet; in fact, we really are still trying to understand this whole disease process.

In December 2007, William Saville, DVM, PhD, Dipl. ACVIM, chair of the Department of Veterinary Preventive Medicine at The Ohio State University’s College of Veterinary Medicine, reported in a study that the parasite that causes EPM spreads through lymph and blood to a number of organs, including the central nervous system, within a matter of days after exposure to S.

How the parasite gets into the central nervous system is a matter for more study.

A study published in December 2007, this one by Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, a professor of medicine in Texas A&M’s Department of Large Animal Clinical Science, identified three factors that increase a horse’s risk of infection: living with cats, use for Western performance or racing, and age greater than 2 years. Cohen cautioned horse owners to consider the context of these findings before changing their horses’ management in the hope of preventing EPM.

While living with cats was a risk factor for EPM, horses in both the EPM and control groups resided with cats.

"It would be a great oversimplification to think that there is sufficient evidence to suggest that removing cats from barns would prevent EPM," emphasized Cohen.

He said while these results contribute to the body of knowledge concerning EPM, controlling these factors to prevent EPM is not realistic.

There are many researchers still interested in this disease, so we can only hope that in the near future a viable vaccine will be developed.

Euthanize vs. Euthanatize

A few years ago The Horse began using the term euthanatize, which was recommended to us as a "more correct usage" of the root term meaning humane death. This term has not "caught on" in the lay press, peer-reviewed veterinary journals, or textbooks, so we are reverting back to euthanize.

Thank you for your input and patience.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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