| 1. NCBI Taxonomy ID: |
| 42890 |
| 2. Disease: |
| Equine protozoal myeloencephalitis |
| 3. Introduction |
| Sarcocystis neurona is the most common cause of equine protozoal myeloencephalitis (EPM) in horses in America. It is a single celled parasite belonging to the group called coccidia (Apicomplexa: Sarcocystidae) with opossums as the definitive hosts and a variety of mammals as aberrant or natural intermediate hosts . Only asexual stages have been identified in the aberrant intermediate hosts, and they are confined to the brain and spinal cord, and any part of the central nervous system (CNS) may be affected. In histologic sections of CNS, individual merozoites are about 3-5 um long and contain a single, centrally located vesicular nucleus. The sarcocysts are microscopic (~700 um long) with a 1-3 um thick sarcocyst wall. The bradyzoites are slender and tiny (~ 5 um long). Sarcocystis neurona sporocysts from opossum faeces are ~ 10 x 8 um in size (USDA Agricultural Research Service: Sarcocystis neurona). |
| 4. Microbial Pathogenesis |
|
The pathogenesis of EPM is not clear because the complete life cycle is unknown. Sarcocystis neurona can parasitize all regions of the CNS, from the anterior cerebrum to the end of the spinal cord. Sarcocystis neurona schizonts and merozoites are found in neurons, mononuclear cells, glial cells, and perhaps other neural cells (USDA Agricultural Research Service: Sarcocystis neurona). |
| 5. Host Ranges and Animal Models |
| Opossums (Didelphis virginiana, D. albiventris) are its definitive (reservoir) hosts and excrete oocysts and sporocysts (environmentally resistant stage)in their feces. Raccoons, armadillos, sea otters, skunks, cats and possibly other mammals are intermediate hosts (USDA Agricultural Research Service: Sarcocystis neurona). |
| 6. Host Protective Immunity |
| Cell mediated immunity is an important component of controlling this intracellular parasite (Marsh et al., 2004). |
