Equine Protozoal Myeloencephalitis

Equine protozoal myeloencephalitis (EPM) is a commonly diagnosed neurologic condition of the horse that was originally described in 1964 by J. Rooney's "segmental myelitis". Consistent with the geographic range of the opossum definitive hosts, EPM caused by S. neurona is a disease of North, Central, and South America. Most horses with a diagnosis of EPM outside this region appear to have spent some time in the endemic area. Gross lesions in the central nervous system (CNS) of EPM horses are sometimes inapparent. When present, lesions are random and multifocal and are more commonly seen in the spinal cord but can occur in the brain or brainstem. Once the organism has infected the nervous system, it leads to localized inflammation with clinical neurologic abnormalities that are dependent upon the anatomic site of the infection in the CNS. The use of antiprotozoal compounds is the cornerstone of treatment for EPM.