It’s dangerous. It’s debilitating. And sometimes it’s deadly. It’s equine protozoal myeloencephalitis (EPM), and researchers have been studying this neurologic disease for years to try to understand it better. Scientists have made great strides in their comprehension of how the causative agents work, what they do to the body, and how to prevent them from debilitating a horse to the point of requiring euthanasia.

At the 2011 American College of Veterinary Internal Medicine Forum, held June 15-18 in Denver, Colo., Frank Andrews, DVM, MS, Dipl. ACVIM, professor at Louisiana State University School of Veterinary Medicine, presented the latest information in an overview of EPM.

Andrews began by reviewing the life cycle of EPM’s causative protozoa (Sarcocystis) as it passes from the feces of opossum and other less common host species and contaminates feed or forage that is ingested by the horse. Once in the horse’s intestinal tract, protozoal sporocysts reproduce, changing form into merozoites, which migrate into the blood where they become engulfed by white blood cells. In this way, protozoa enter the central nervous system (CNS) and do damage within the brain and/or spinal cord.

"The insidious onset of clinical signs can take a while to appear," explained Andrews