Ask the Vet: Equine Protozoal Myeloencephalitis (EPM)

Courtesy of AAEP Answered by Sandi Farris, DVM, Harmony Veterinary Services, LLC

Question: If scat is removed from pastures, does it greatly reduce chances of horses contracting EPM?

Answer: Pastures can be contaminated with Sarcocystis oocysts from the feces of infected possum or other wildlife vectors. Certainly, removing feces from the grass would be ideal to prevent contamination. Unfortunately, it would be difficult, if not impossible, to clear all fecal material from a pasture or paddock. Managing the possum population by humanely removing the animals from the area or preventing access to a paddock or pasture is recommended.

Pastures with areas of woods or bordering wooded areas will be more likely to have an opposum population. Keep garbage or other possum feed sources secured and away from the paddocks and pastures. Stalls and barns may be cleaned with power washers to remove feces and oocysts. Secure your grain and hay sources to prevent possum access and monitor horses closely for potential EPM symptoms. Managing the opposum population is your best bet for decreasing your horses’ exposure to EPM organisms.

Question: My horse went through treatment for EPM two years ago and has recovered. He is now 25-years-old. Is there any supplement he should be receiving that would help resist a relapse?

Answer: Vitamin E is an excellent antioxidant that helps support muscle and nerve health and function. It, as well as other antioxidants and anti-inflammatories such as MSM, are not specific to reducing the chances of contracting EPM, but do improve the health and immune strength of a horse. Some studies suggest that thiamine or folic acid may improve the nerve health, especially following medical treatment of EPM, and lower the chance of a relapse.

A healthy horse that receives well-balanced nutrition, consistent and appropriate exercise, and has quality shelter and care has a lowered risk of contracting EPM. Managing pasture and feed contact with opposums or other vectors decreases the risk of exposure. Use critical thinking about any supplement that claims to be a definitive prevention for EPM or other disease. Keeping your horse healthy is the best prevention we have!

Question: I have a mare that had EPM 5 years ago. She could hardly stand or walk, but was treated aggressively for the condition and recovered. In fact, she was able to return to racing and had no reoccurance. Currently, she is in foal and due any day. Could her previous bout with EPM affect the foal?

Answer: The EPM research group at UC Davis have found that the organisms of EPM, Sarcocystis and Neospora, do indeed transmit from the mare to the foal in utero. A previously treated mare that is no longer showing neurologic signs, can transmit the organisms under times of stress such as late gestation, directly to the foal. The mare herself can have a relapse of EPM at this high stress time.

While infected foals have been treated successfully from birth for the EPM organisms, the risk of neurolgic deficits and loss of performance warrants serious consideration if you decide to breed a previously infected mare. If your mare is due to foal, be prepared by speaking with your veterinarian about how to manage and treat a likely EPM positive foal for best results.