Equine Protozoal Myeloencephalitis (EPM)

Equine Protozoal Myeloencephalitis (EPM) is a central nervous system disease that is caused by the protozoal organism Soarcocystis neurona.  EPM can affect equines of any age, sex, and in any location in the United States.  The organism reproduces in the opossum and is passed out in the feces.  Horses pick up the organism by eating opossum feces dropped in feed or hay.  The horse is noncontagious, but can develop the disease.  Not all horses exposed to EPM will show clinical signs and some may develop an immunity and fight off the disease.

Soarcocystis  neurona can be located anywhere in the central nervous system, so a range of signs may be seen.  Sometimes these signs mimic other neurological diseases.  The disease can take from 2 weeks to 2 years from exposure time until symptoms are seen.

Clinical signs include:

• Incoordination, stiff movements, abnormal gaits or lameness
• Incoordination and weakness is worse when going up or down slopes or when the head is elevated
• Muscle atrophy along topline and large muscles of the hindquarter
• Facial paralysis
• Difficulty swallowing
• Seizures or collapse
• Abnormal sweating
• Loss of sensation along the face, neck or body
• Head tilt with poor balance

There are tests available to diagnose EPM.  There are pros and cons for each of them, so consult with your veterinarian to determine the best test for you and possible treatments.  There are two treatment options available.  About 60% of affected horses will improve and some will recover completely.  As with most diseases, earlier treatment is more effective.  There is not a vaccine for EPM.

Prevention of EPM includes controlling the contact between opossums and horses in and around the barn.  Keep all feed covered and out of reach (including cat feed).  Know the signs of the disease and involve your vet early if your horse starts having symptoms.

Here are two articles with more in-depth information: University of Minnesota Extension and Horse eXtension.