Sarcocystis neurona
An etiologic agent of equine protozoal myeloencephalitis (EPM)

Test code: X0004 - Ultrasensitive qualitative detection of Sarcocystis neurona by real time polymerase chain reaction

Equine protozoal myeloencephalitis (EPM), also known as "equine protozoa myelitis" is primarily caused by the apicomplexan parasite Sarcocystis neurona. EPM is the most commonly diagnosed neurologic disease of the horse in the US (Dubey et al., 2001). Based on reported surveys from individual horse owners, EPM has been labeled as the most important infectious disease facing the equine industry ( NAHMS, 2001). Several surveys conducted in Ohio have revealed greater than 50% (53.6%) of horses with circulating S. neurona antibodies (Saville et al., 1997). Opossums (Didelphis virginiana) serve as definitive hosts for S. neurona in the US and are responsible for shedding infective S. neurona sporocysts (Fenger et al., 1997; Dubey and Lindsay, 1998). However, it is not clear how the opossum became infected because hosts harboring sarcocysts have not been identified. Recently, S. neurona sarcocysts have been identified in the muscles of cats, raccoons, armadillos, sea otters and skunks. Recent studies from Michigan and Florida have reported S. neurona antibodies in 5% of domestic cats. A subsequent study has confirmed domestic cats to be natural carriers of this parasite (Stanek et al., 2003).

Horses are an aberrant intermediate host of S. neurona. Sporocysts are eaten, pass into the small intestine and excyst there. The infective stage of the organism, the sporozoite, then enters the horse's blood stream. In some horses, these undergo several replicative cycles in endothelial cells (in blood vessels), becoming tachyzoites, and migrate to the central nervous system. They replicate asexually within neurons and microglial cells without forming tissue cysts. In the central nervous system of the horse, they slowly divide and grow, gradually destroying the nervous tissue, causing incoordination and the other clinical signs that result from EPM. At this stage, the organism found in horses cannot be transmitted to other horses. Because the organism does not encyst in horse tissues, it cannot be transmitted to opossums, even if an opossum were to eat the tissue. Therefore, the horse is a dead end host for the protozoan.

Utilities:

• Confirm the disease causing agent
• Shorten the time required to confirm a clinical diagnosis of S. neurona infection.
• Ensure that animal populations are free of S. neurona
• Early prevention of spread of this protozoan
• Minimize human exposure to this protozoan
• Safety monitoring of biological products that derive from host animals

References:
Dubey, J.P. and Lindsay, D.S. (1998) Isolation in immunodeficient mice of Sarcocystis neurona from opossum (Didelphis virginiana) faeces, and its differentiation from Sarcocystis falcatula. Int. J. Parasitol. 28:1823–1828..
Dubey, J.P., Lindsay, D.S., Saville, W.J.A., Reed, S.M., Granstrom, D.E. and Speer, C.A. (2001) A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM). Vet. Parasitol. 95: 89–131.
Fenger, C.K., Granstrom, D.E., Langemeier, J.L. and Stamper, S. (1997) Epizootic of equine protozoal myeloencephalitis on a farm. J. Am. Vet. Med. Assoc 210: 923–927.
NAHMS (2001). Equine Protozoal Myeloencephalitis (EPM) in the US. APHIS:VS, CEAH, National Animal Health Monitoring System. USDA, Fort Collins, CO.
Saville, W.J.A., Reed, S.M., Granstrom, D.E., Hinchcliff, K.W., Kohn, C.W., Wittum, T.E. and Stamper, S. (1997) Prevalence of serum antibodies to Sarcocystis neurona in horses residing in Ohio. J. Am. Vet. Med. Assoc. 210:519–524.
Stanek, J.F., Stich, R.W., Dubey, J.P., Reed, S.M., Njoku, C.J., Lindsay, D.S., Schmall, L.M., Johnson, G.K., LaFave, B.M. and Saville, W.J. (2003) Epidemiology of Sarcocystis neurona infections in domestic cats (Felis domesticus) and its association with equine protozoal myeloencephalitis (EPM) case farms and feral cats from a mobile spay and neuter clinic. Vet Parasitol. 117:239-49.

Specimen requirements: 1 ml whole blood in EDTA (purple top) or ACD (yellow top) tube, or 0.5 ml cerebrospinal fluid or tissue, shipped overnight at room temperature; or frozen tissue shipped frozen.

For specimen types other than those listed here, please call to confirm specimen acceptability and shipping instructions.

For all specimen types, if there will be a delay in shipping, or during very warm weather, refrigerate specimens until shipped and ship with a cold pack unless more stringent shipping requirements are specified. Frozen specimens should be shipped so as to remain frozen in transit. See shipping instructions for more information.

Turnaround time: 2 business days

Methodology: Qualitative real time PCR

Normal range: Nondetected