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 TheHorse.com, leading us to wonder about the occurrence of this disease. A poll about EPM conducted on TheHorse.com 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