Falabella Breeders & Owners Society

Falabella Breeders Digest   May 2003 Issue

EPM: Equine Protazoal Myeloencephalitis  by Wendy Strong

 Equine Protazoal Myeloencephalitis, otherwise known as EPM, or possum disease is a neurological disease caused by parasites in opossum feces which may contaminate hay or grass consumed by our horses.

EPM was first discovered in Kentucky during the early sixties when Standardbred owners noticed neurological problems in their horses.  This disease was gradually spread throughout the USA and Canada when possums migrated.

Horses affected display neurological symptoms of having a wobbly gait and clumsiness.  Lack of coordination is the most common symptom.  This disease sometimes effects muscle atrophy in the hind end, shoulders, face and tongue.    If the face and tongue is involved, the horse will have great difficulty eating and drinking.  When the disease affects the hind end, the horse will have difficulty walking and backing up and the tail can show no resistance when lifted.

EPM must be diagnosed by a blood test.  Sometimes, horses in the very early stages of the disease will test negative, when they truly have the disease.

There are several treatments for EPM, however none of the treatments are 100%.  One of the most common medications used for treatment is the use of sulfa drugs as well as anti-inflammatories.  Horses must remain on the prescribed treatment for a long period of time to avoid the disease from returning. 

The best precaution against this terrible disease we can offer our horses is to keep opossums out of our barns, especially away from the horse feed and bedding.  However, keeping opossums out of our horse pastures can present a bit of a challenge.  However a good dog may be able to keep opossums at a distance, or at least alert owners that these disease carrying creatures are near.

Hopefully one day there will be a preventive vaccine for this nasty disease.

I have learned about EPM in an unfortunate manner.  I noticed China one of our older broodmares lying around much of the time and she appeared to be very lethargic. And when I got her up on her feet, she seemed rather stiff in the back end.  Since this mare is now 16 years old, I first suspected arthritis.   I had my vet check her for parasites, laminitis and arthritis.  But a blood test sent to Kentucky confirmed that she indeed had EPM.  (And we did find an opossum living in our hay storage building).  We have been treating China for six weeks with medication and hope she will have a full recovery.