Reduce Your Horse's Exposure to Equine Protozoal Myeloencephalitis as Summer Turns to Fall

Opposum standing on wall - Carrier of protozoal microorganism causing EPM
Opposum standing on wall - Carrier of protozoal microorganism causing EPM Wolfman

Newsdate: Monday, August 8, 2022, 11:00 am
Location: GILROY, California

Equine protozoal myeloencephalitis (EPM) is a progressive and potentially fatal infection of the central nervous system that most often occurs in the summer and fall seasons. It is caused by a single-celled protozoal microorganism, most commonly S. neurona, and is primarily transferred by opossums through their feces.

Horse drinking from a pool of contaminated water.

Horse drinking from a pool of contaminated water

Equine protozoal myeloencephalitis is a progressive and potentially fatal infection of the central nervous system that most often occurs in the summer and fall seasons.
© 2016 by Peter Gudella New window.

Researchers estimate that approximately 30 to 80% of the U.S. horse population has come in contact with the parasite and produced antibodies that can be measured in their blood. However, not all horses exposed become infected or develop clinical signs. In fact, the incidence of EPM may be less than 1%.

There is no way to prevent EPM as no vaccine exists. The best way to reduce the risk of your horse contracting the disease is to minimize exposure to opossum feces. All age groups of horses may be affected, however, EPM is most common in younger horses 1 - 7 years of age.

Risk factors include:

  • Presence of opossums
  • Previously infected horses on premises
  • Summer and fall seasons (winter has fewer cases)
  • Stress - including shipping or recent illness
  • Wooded terrain near pastures
  • Feed and hay accessible to opossums  

While EPM is nearly impossible to prevent, controlling bird and opossum populations can help:

  • Keep opossums out of barns and away from feed and bedding
  • Keep tight covers on grain
  • Feed horses processed grain steam-crimped and pelleted to kill
    parasites
  • Install mesh wire fencing with a “hot wire” around the outside to deter opossums (they climb instead of dig)
  • Dispose of dead animals, including birds, small rodents and opossums, to prevent the spread of parasitic eggs.
  • Limit bird populations in the barn

About the Author

Flossie Sellers

Author picture

As an animal lover since childhood, Flossie was delighted when Mark, the CEO and developer of EquiMed asked her to join his team of contributors.

She enrolled in My Horse University at Michigan State and completed a number of courses in everything related to horse health, nutrition, diseases and conditions, medications, hoof and dental care, barn safety, and first aid.

Staying up-to-date on the latest developments in horse care and equine health is now a habit, and she enjoys sharing a wealth of information with horse owners everywhere.

Subscribe