Equine protozoal myeloencephalitis (EPM) is a disease that affects the central nervous system of horses. It is caused by a protozoal infection that is brought about by the apicomplexan parasites Sarcocystis neurona or Neospora hughesi. Most cases are caused by S. neurona. The lifecycle and transmission of N. hughesi is not well understood.[1] The parasites create lesions in both the brain and spinal cord of the affected horses leading to neurological issues.[2] Most horses infected with S. neurona do not exhibit neurological symptoms consistent with EPM.[citation needed]
^Dubey, J. P. (May 2022). "Sarcocystis neurona, Neospora spp. and Toxoplasma gondii infections in horses and equine protozoal myeloencephalitis (EPM): five decades of personal experience, perspectives and update". Parasitology. 149 (6): 717–728. doi:10.1017/S0031182021002055. ISSN0031-1820. PMID35260209.