Sarcocystis neurona is an intracellular, apicomplexan protozoan parasite that is the etiological agent of equine protozoal myeloencephalitis (EPM) in horses.
S. neurona infects other animal species besides horses and requires two specific types of hosts (definitive and intermediate) to complete its life cycle.
The opossum (Didelphis virginiana) is the definitive host and is where S. neurona undergoes its sexual cycle. Sporocysts of S. neurona get released in their feces.
Horses serve as intermediate hosts. S. neurona asexual reproduction takes place in the horse's central nervous system.
S. neurona is only a concern for horses living in the Americas as this is the geographic reach of the opossum.
