How can you keep your horses safe from EPM?

The best way to keep your horses healthy is prevent them from getting sick. Sounds absurdly simple, right? In theory, this works. But in the real world of trying to protect horses from diseases such as equine protozoal myeloencephalitis (EPM), it isn’t always that simple.


Sharon Witonsky, DVM, PhD, Dipl. ACVIM, associate professor in the Department of Large Animal Clinical Sciences at the Virginia-Maryland Regional College of Veterinary Medicine, describes the critical role immune response plays for a horse to mount effective protection against an invader: “We know, based on mouse models, that cell-mediated immunity is critical for protection. An optimal immune response would be one that stimulates both antibodies (in the serum) as well as cell-mediated immunity.”

So how does this relate to EPM? Witonsky explains, “Antibodies can potentially coat S. neurona (the protozoan parasite Sarcocystis neurona that causes EPM) and stimulate complement- mediated killing,” which is one method the immune response has of eliminating foreign proteins and antigens. “The cell-mediated immune response also results in killing of S. neurona. Ideally, S. neurona would be killed before entering the central nervous system.”

Debra Sellon, DVM, PhD, Dipl. ACVIM, professor of equine medicine in Washington State University’s Department of Veterinary Clinical Sciences, further explains this arm of the immune system that influences blockade of infection: “Currently, most investigators believe that production of gamma interferon is especially important for protection against disease. Gamma interferon can be produced by many different cell types, and it is unclear which of these cell types are most important for protection of horses against EPM. Most likely, a cell-mediated response from lymphocytes (sp