Equine Protozoal Myeloencephalitis - What is EPM?

Horses are known for being strong and graceful, but a hidden danger called Equine Protozoal Myeloencephalitis—or EPM for short—can change that quickly. This very common neurological disease attacks a horse's central nervous system, targeting both the brain and the spinal cord. EPM is caused by two microscopic parasites, Sarcocystis neurona and Neospora hughesi. While both are dangerous, Sarcocystis neurona is the main culprit behind most cases. When these tiny organisms get into a horse's system, they can cause serious coordination problems, making early detection vital for every horse owner.

Understanding how a horse catches EPM involves looking closely at local wildlife. While multiple animals like skunks, domestic cats, and armadillos carry the parasite, the opossum is the only definitive host. Opossums become infected by scavenging on these carrier animals and then spread the parasite into the environment through their feces. Horses then accidentally contract EPM by ingesting contaminated feed or water. Fortunately, horses are incidental hosts, meaning they cannot pass the parasite back to opossums and cannot spread the disease directly to other horses. Interestingly, exposure is incredibly common, with 50% to 90% of horses in the United States testing positive for the parasite. However, actually developing the clinical disease is rare, as fewer than 1% of exposed horses ever show symptoms.

Recognizing the signs of EPM early can save your horse's career and life. The disease can show up in many ways, including uneven gaits, a drooping face, difficulty swallowing, or shifting lameness. To help you remember the most critical warning signs, just think of the acronym STALL:

• S – Stumbling and general incoordination

• T – Tilted head or a drooping face

• A – Asymmetrical muscle loss, especially in the hindquarters

• L – Lameness that seems to mysteriously shift from leg to leg

• L – Leaning or leaning to one side while standing or walking

If you notice any of these symptoms, you must contact your veterinarian immediately for a firm diagnosis. While EPM can be treated and managed with your vet's help, it is important to know that it is not always fully cured. There are currently three FDA-approved treatments available, and getting started quickly is vital since horses see the greatest amount of health improvement within the very first four weeks of starting medication. Overall, about 60% to 70% of horses show significant improvement with treatment, and roughly 15% to 25% make a complete recovery. However, owners should stay vigilant, as relapses occur within two years in about 10% to 20% of horses.

Even though EPM exposure is incredibly common, you can take active steps on your farm to prevent it. Since pest and feed management are your best lines of defense, focus on keeping local wildlife far away from your horse's daily environment. Always use tightly sealed containers to store your grain and supplements so critters cannot break in. Be sure to clean up any feed spills or trash immediately to remove easy food sources. You should also scrub out feeders and waterers regularly to keep them fresh and uncontaminated. Make it a habit to keep your hay covered and securely stored away from roaming animals. Finally, walk your property often to check for any clear signs of wildlife, including hidden denning sites, animal feces, or evidence of chewed materials.

Your horse's health depends on a clean environment and a watchful eye. By protecting your feed room today and remembering the STALL acronym, you can keep your partner safe, healthy, and on the right track.