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)
From The Horse Journal:
  • Battling EPM: Choose your weapons, March 2005
  • EPM Continues to Defy Logic, February 2001
  • EPM in Horses, August 2007
  • EPM is Becoming a Catch-All Diagnosis, December 2002
  • Is an EPM Cure Realistic? August 2004

Further Reading for Your Veterinarian

Mackay RJ, Tanhauser ST, Gillis KD, et al. Effect of intermittent oral administration of ponazuril on experimental Sarcocystis neurona infection of horses. Am J Vet Res. 2008 Mar;69(3):396-402.

Cohen ND, Mackay RJ, Toby E, et al. A multicenter case-control study of risk factors for equine protozoal myeloencephalitis. J Am Vet Med Assoc. 2007 Dec 15;231(12):1857-1863.

Duarte PC, Ebel Ed, Traub-Dargatz J, et al. Indirect fluorescent antibody testing of cerebrospinal fluid for diagnosis of equine protozoal myeloencephalitis. Am J Vet Res. 2006 May;67(5):869-876.

About Dr. Lydia Gray

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Mollie and Eden
I started riding when I was 9 years old and quickly got swept up into the competitive hunter/jumper world. I showed my first pony, Chloe, in the Small Pony Hunter divisions were we competed at shows like Fairfield Hunt Club, Old Salem, HITS, and West...

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