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EPM In Horses (Equine Protozoal Myeloencephalitis)

By: Dr. Lydia Gray

SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.

Brief Description

Equine Protozoal Myeloencephalitis (EPM) is a disease of the central nervous system (brain and spinal cord) caused by the protozoa Sarcocystis neurona. EPM is transmitted by the opossum through intermediate hosts, also known as carriers, which may include birds, cats and other animals.

EPM is characterized by:

  • Ataxia (incoordination)
  • Asymmetry (worse on one side of the body than the other)
  • Atrophy (loss of muscle mass)

Supplements that May Lend Support

Many veterinarians suggest horses undergoing treatment for EPM be supplemented with Vitamin E to support their muscle and nervous tissue. Other antioxidants as well as natural anti-inflammatories such as MSM, Omega 3 Fatty Acids and certain herbs may be beneficial in reducing damage to cells as the protozoa are destroyed.

Possible Diagnostic Tests

In addition to a complete physical examination, your veterinarian will perform a series of specific neurological tests such as crossing legs, pulling the tail, blindfolding, etc. Because there are many conditions that can cause neurological signs, additional tests such as x-rays, bloodwork and spinal tap may be required to rule out things like “wobblers disease” or herpes virus.

Prescription Medications Available

There are currently three FDA-approved medications on the market to treat EPM: Marquis® (ponazuril), Navigator® (nitazoxanide) and ReBalance™ (sulfadiazine and pyrimethamine). A fourth product, Protazil (diclazuril) has been approved by the FDA but is not yet on the market.

In addition, some veterinarians recommend the prescription medications bute (phenylbutazone), Banamine® (flunixin meglumine) or Prednis Tabs® (a corticosteroid) as anti-inflammatories, to help manage pain during treatment.

Other Management Suggestions

Since the opossum is the definitive host of the protozoa that causes EPM, and birds, cats and other animals are carriers, measures to keep these animals away from your horses’ food and water sources may reduce the risk of infection.

Questions to Ask Your Veterinarian

  • Will my horse relapse?
  • Should I use one of the prescription products as a preventative?
  • Are the other horses in the barn likely to develop EPM?

Additional Resources

Further Reading for You

From the SmartPak Ask the Vet Blog:
Horses and Equine Protozoal Myeloencephalitis (EPM)


About Dr. Lydia Gray

Healthy Horses  ❤  Happy Riders