Equine protozoal myeloencephalitis.

Equine protozoal myeloencephalitis (EPM) is a common neurologic disease of horses in the Americas. Horses with EPM most commonly have abnormalities of gait, but they also may present with signs of brain disease. The disease ranges in severity from mild lameness to sudden recumbency, and clinical signs usually are progressive. A causative agent, Sarcocystis neurona, has been isolated from affected horses, and serologic surveys suggest that approximately 50% of horses in the United States have been exposed. EPM is considered a treatable disease, although the response to antimicrobial treatment often is incomplete. This article highlights new information about the life cycle of S. neurona and reviews the literature regarding diagnosis, clinical signs, and treatment of the disease.