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Learn to Recognize the Symptoms of EPM
Equine Protozoal Myeloencephalitis (EPM) is a master of disguise. This serious disease, which
attacks the horse’s central nervous system, can be difficult to diagnose because its signs often
mimic other health problems in the horse and signs can range from mild to severe. More than 50
percent of all U.S. horses have been exposed to the parasite that causes EPM. Horses can come
into contact with the parasite while grazing or eating feed or drinking water contaminated by
opossum feces. Fortunately, not all horses exposed to the parasite develop the disease.
The clinical signs of EPM can be quite varied. Clinical signs are usually asymmetrical (not the
same on both sides of the horse). Actual signs may depend on the severity and location of the
lesions that develop in the brain, brain stem or spinal cord.
If left undiagnosed and untreated, EPM can cause devastating and lasting neurological damage.
Use this checklist of symptoms from the American Association of Equine Practitioners (AAEP)
when assessing your horse’s condition for the possibility of EPM:
• Ataxia (incoordination), spasticity (stiff, stilted movements), abnormal gait or lameness.
• Incoordination and weakness which worsens when going up or down slopes or when head
is elevated.
• Muscle atrophy, most noticeable along the topline or in the large muscles of the
hindquarters, but can sometimes involve the muscles of the face or front limbs.
• Paralysis of muscles of the eyes, face or mouth, evident by drooping eyes, ears or lips.
• Difficulty swallowing.
• Seizures or collapse.
• Abnormal sweating.
• Loss of sensation along the face, neck or body.
• Head tilt with poor balance; horse may assume a splay-footed stance or lean against stall
walls for support.
Contact your veterinarian immediately if you suspect your horse has developed EPM. The sooner
treatment begins, the better the horse’s chances for recovery. For more information on methods of
prevention and the treatment options for EPM, ask your equine veterinarian for a copy of the
“EPM: Understanding this Debilitating Disease” client education brochure, provided by the AAEP
in partnership with Bayer Animal Health, an AAEP Educational Partner. Additional information
also can be found on the AAEP’s website www.aaep.org/horseowner.
Permission for use is granted with attribution given to the AAEP and Bayer Animal Health.