Information provided by Dr. Robert MacKay, Veterinarian of UF Large Animal Medicine, Professor, DACVIM, PhD, BVSc (Dist). Dr. Robert MacKay has been featured in articles about EPM and at the American Association of Equine Practitioners conventions.

What is EPM?

EPM stands for equine protozoal myeloencephalitis and is a common neurological disease of horses in the Americas.

What are the clinical signs of EPM?

Horses with EPM most commonly have abnormalities of gait but also may present with signs of brain disease. The disease ranges in severity from mild lameness to sudden recumbency and clinical signs usually are progressive.

Checking neurologic function as part of an equine neurologic examination at UF

Signs noticed at the walk or during a neurologic examination include any to all of the following:

  • Pelvic sway
  • Asymmetric stride length
  • Toe dragging
  • Circumduction of the hindlimbs
  • Hypometria (“floating” or “marching”) of the forelimbs
  • Muscle atrophy
  • Signs of brain disease such as a tilted head, beating movements of the eyes, or paralysis of one side of the face

Signs noticed during breaking and/or training:

  • Frequent bucking
  • Head tossing
  • Excessively high head carriage
  • Difficulty maintaining a specific lead or changing leads
  • Difficulty negotiating turns

What causes EPM?

The definitive host of the EPM protozoa (an animal that can carry and reproduce the protozoa and infect other organisms) is the opossum. The opposum passes infective sporocysts with feces. There are several intermediate hosts (animals that can carry but cannot reproduce the protozoa on their own) such as the 9-banded armadillo, the striped skunk, and the raccoon. The intermediate hosts can spread the disease to other opossums, but only the opossum can infect others. It is presumed that horses ingest infective opossum sporocysts with feed or water.

Can an infected horse spread EPM?

No. Horses are referred to as a “dead end host” for EPM, meaning that they can become infected but cannot infect others.

How can I prevent EPM in my horse?

Opossums sporocysts can be found in feed or water. Opossums are omnivores, and are attracted to grains, moist or dry cat or dog food, fruit or garbage. Therefore, horse feed and pet food should not be left out and open feed bags and garbage should be kept in closed galvanized metal containers, bird-feeders should be eliminated, and fallen fruit should be removed. Steam cleaning has been shown to kill sporocysts, so feed and water containers could be cleaned by this technique. Opossums can be trapped and relocated or scared off by a dog.

It is probable that sporocysts are distributed from the point of deposition by birds and insects, so it may be prudent to control populations of these potential vectors, at least within horse barns.

What if my horse gets EPM?

EPM is considered a treatable disease although the response often is incomplete. If you suspect your horse has EPM or is exhibiting any of the clinical signs listed above, contact your veterinarian or the UF Large Animal Hospital veterinarians at (352) 392-2229 and visit our Contact Us page for more information.

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