EPM: Three letters that horse owners have come to dread—and for good reason.
Equine protozoal myeloencephalitis is one of the most frustrating diseases a horse can contract. Called a “master of disguise” by the American Association of Equine Practitioners, EPM can mimic many other health problems, with signs ranging from mild to severely disabling to life-ending.
The disease that eventually came to be called EPM was first recognized in the 1960s and since then researchers have made steady progress in understanding the responsible organisms, modes of transmission and the physiological effects on horses. Most importantly, three Food and Drug Administration-approved medications have been developed to treat EPM in horses: Marquis (ponazuril), Protazil (diclazuril) and ReBalance (sulfadiazine/pyrimethamine).
Nonetheless, EPM remains a major horse health concern and questions persist—among owners and researchers alike—about the nature of the disease, the horses most likely to be affected and the best way to help them recover. To find out the latest thinking on these questions and more, we asked three experts to share their insights.
1. EPM was a “hot topic” about 20 years ago—the subject of much research, professional chatter and horse owner worry. Now we are hearing less about it. Why?
“Probably the reason horse owners are hearing less about it now is because we have effective medications, compared with 20 years ago,” says Sarah Colmer, VMD, a board-certified internal medicine specialist at the University of Pennsylvania’s New Bolton Center. “There are three FDA-approved options for treating EPM, and cases can be diagnosed and treated early in the course of infection. That said, there is still much to be done.
Other diseases may be grabbing the attention of horse owners either because of scientific breakthroughs or prevalence," says long-time EPM researcher Sharon Witonsky, DVM, PhD, DACVIM. “We have definitely made improvements in understanding EPM in the last several years, but there haven’t been transformative increases in our knowledge and associated practical applications,” explains Witonsky, who is a professor at Virginia Tech in Blacksburg. “By comparison we are hearing more about other concerns—Lyme disease, the neurologic form of equine herpesvirus and a few other diseases, which may impact the attention EPM is getting.”
Both Colmer and Witonsky stress, however, that EPM is still the subject of significant ongoing research, with new findings to be published soon. “People can keep an eye out for some exciting updates,” Colmer says.
2. We’ve known for years that the protozoal parasite is the primary causal organism for EPM and that opossums are key to their life cycle. another protozoan that can cause EPM, still has an unelucidated life cycle, and the mode of transmission is uncertain. Have there been
