Equine protozoal myeloencephalitis (EPM) is a protozoal disease common to horses, particularly in the southern states. EPM is hosted by the opossum and is caused by a parasite called Sarcocystis neurona. This particular horse illness causes mostly neurological problems and can become serious if left untreated.
The most common symptom of EPM is a notable disconnection between a horse's front end and back end. He might move as though he were drunk, unsure of where to put his feet. Muscular atrophy is one of the advanced symptoms of this horse disease.