what is epm in horses

Equine Protozoal Myeloencephalitis (EPM) is a disease that affects the central nervous system of horses and is caused by the apicomplexan parasite Sarcocystis neurona. The disease is not transmitted from horse to horse, but rather the protozoa are spread by the definitive host, the opossum, which acquires the organism from cats, raccoons, skunks, and armadillos. More than 50% of all horses in the United States may have been exposed to the organism that causes EPM. The most common symptoms of EPM are ataxia, general weakness with muscle spasticity, and incoordination, muscle atrophy, and loss of feeling around the body. However, these symptoms are not specific to EPM and are common to many other neurological disorders. Definitive diagnosis of EPM relies on postmortem examination of neural tissue, and no test in the live horse is currently considered definitive. Therefore, EPM is diagnosed based on a combination of a thorough neurologic examination, evaluation of serum and/or cerebrospinal fluid (CSF) for the presence of antibodies to S. neurona and/or N. hughesi, and the elimination of other neurological disorders. If left undiagnosed and untreated, EPM can cause devastating and lasting neurological deficits. Preventative approaches include decreasing stress and reducing exposure to opossum feces.