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Equine Protozoal Myeloencephalitis (EPM)

This educational webinar on Equine Protozoal Myeloencephalitis (EPM) was presented by Dr. Sarah Colmer from the University of Pennsylvania New Bolton Center. EPM continues to plague horses in North, Central, and South America, causing neurological deficits that threaten athletic careers and lives. Improve your understanding of the EPM, learn more about diagnostics, treatment options, and how to minimize your horse's chance of an infection.


  • EPM is caused by an infection with one of two parasites- Sarcocystis neurona and, less commonly, Neospora hughesi.

  • Horses most often become infected by consuming opossum feces containing S. neurona in pastures, barns, hay, water sources, etc.

  • The parasite migrates through the horse’s body before taking residence in the brain and/or spinal cord.

  • Many horses in North America (up to 85%) have antibodies against S. neurona, indicating they have been exposed to the parasite, even if they have not shown signs of infection.

  • Clinical signs of EPM vary greatly between individual horses and may include incoordination, weakness, spasticity, decreased reflexes, depression, head tilt, facial nerve paralysis, difficulty swallowing, upper airway dysfunction, seizures, etc.

  • EPM is challenging to diagnose, and all other causes of neurologic disease must be excluded before making a presumptive diagnosis of EPM.

  • If left undiagnosed and untreated, EPM can cause devastating and lasting neurological deficits. Success rates for treated horses are high.

  • Many horses with EPM will improve, and a smaller percentage will recover completely, but up to 20% of cases may relapse within two years.

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