Battle Against EPM Showing Progress

Progress in the battle against equine protozoal myeloencephalitis (EPM) was reported during an annual convention of the American Association of Equine Practitioners (AAEP) in Phoenix, Ariz., on Dec. 7-10. Researchers from the University of Kentucky detailed their work with an experimental medication, diclazuril, saying that while it is not effective in every case, it seems to have advantages over the currently recommended treatment regimen.

The drug is not yet approved for use in the United States. The University of Kentucky has been given special permission to use it for a research study on EPM. Horses chosen for the study all tested positive for the EPM parasite and all had suffered relapses after undergoing conventional therapy.

Of the 74 horses involved in the study, 63 completed the study's recommended 21-28 day course of treatment with diclazuril. Seventy-five percent showed improvement: 25 percent did not improve. In addition, the University also collected information on 19 horses which have returned to athletic performance following treatment. Five moved up in class: six remained at the same level and eight dropped in class.

Dr. David Granstom, an authority on EPM who formerly worked at the University of Kentucky and is the author of a new book, Understanding EPM, said the rate of positive response to treatment with diclazuril is similar to that obtained using pyrimethamine and sulfa drug combination. However, diclazuril may prove to be a more attractive option for a couple of reasons.

The recommended treatment period is shorter with diclazuril-only three to four weeks compared to four months or more with standard therapy. Dr. Frank Andrews of the University of Tennessee presented evidence at the convention that the treatment length for standard therapy should be extended to at least seven months in order to clear antibodies to the EPM-causing protozoan from the cerebrospinal fluid.

In addition, while relapses are common with the other drugs, they don't appear to be a problem with diclazuril. "The ones that relapsed appeared to do so because they were given an ineffective dose of diclazuril," Granstom said. Using diclazuril in combination with pyrimethamine also looks promising, Granstom added.