EPM: The most common neurological disease in horses.




While all horses are susceptible to contracting EPM, it appears that horses used for racing and western performance horses may be more likely than others.

EPM is a progressive and potentially fatal infection of the central nervous system. It is caused by a single-celled protozoal microorganism, most commonly S. neurona, and is primarily transferred by opossums through their feces.

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. Risk factors include:

  • All age groups may be affected, however, EPM is more common in horses 1 - 7 years of age
  • 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
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