Equine protozoal myeloencephalitis (EPM) is a neurologic disease of horses caused by the apicomplexan protozoa Sarcocystis neurona, an organism which is thought to be genetically identical to Sarcocystis falcatula. Sarcocystis neurona has a twohost life cycle which is perpetuated when a carnivore or an omnivore consumes the flesh of an infected intermediate host containing sarcocysts (the encysted stages of the parasite). The opossum is the primary host of the parasite, while birds are intermediate hosts; the horse is merely an aberrant, deadend host.