How Do Horses Get EPM?

Find out the most common way horses contract equine protozoal myeloencephalitis, or EPM.
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How Do Horses Get EPM?
The main protozoan that causes EPM, Sarcocystis neurona, is found in the scat of some opossums. | Photo: Thinkstock
Q: How do horses get equine protozoal myeloencephalitis (EPM), and what is the best way to prevent it?

—Emilee

A: The main protozoan that causes EPM, Sarcocystis neurona, is found in the scat of some opossums. The horse eats feed (hay or grain/concentrates) that is contaminated with S. neurona from opossum feces, and the protozoa gains entrance into the horse’s blood through the intestinal tract. (The protozoan Neospora hughesi also causes EPM, but the definitive host is not known).

In most horses S. neurona is killed by the horse’s immune system in the lymph nodes of the intestines. However, in some horses, the EPM protozoa is captured by white blood cells and passed across the blood-brain barrier into the central nervous system, where it infects the nerve cells

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Written by:

Frank M. Andrews, DVM, MS, Dipl. ACVIM, is LVMA Equine Committee professor and director of the Equine Health Studies Program at Louisiana State University’s School of Veterinary Medicine. As an internal medicine specialist, Andrews research interests include equine gastric ulcer disease.

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