Equine protozoal myeloencephalitis: Etiology, diagnosis and treatment - DVM
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Equine protozoal myeloencephalitis: Etiology, diagnosis and treatment
Early identification is key in this widespread neurologic disease



As S. neurona is the critical factor (along with N. hughesi in some cases), it would be advantageous to rid the horse environment of the parasites—similar to trying to eradicate caterpillars to limit mare reproductive loss syndrome. Sarcocystis neurona and N. hughesi, though, are ubiquitous in nature along with their definitive host, the opossum, and numerous intermediate hosts (e.g., cats, raccoons, armadillos, skunks). Management of both hosts and parasites could be used, though it is unlikely to be successful.

"With the parasites being so prevalent in nature, horses may be exposed and reexposed—some horses throughout their lifetimes, or at least for many years," says Morrow. "A horse infected at one time may harbor parasites within the CNS that, under stressors such as transport, at a later time may trigger that individual to develop clinical signs of EPM."

The main veterinary solution is to accurately diagnose the disease and treat it early when possible. The use of the newer diagnostic assays, such as the indirect fluorescent antibody test and the quantitative ELISA based on S. neurona surface antigens (SnSAG 2,3,4), along with the newer coccidiostats, ponazuril and diclazuril, will go a long way until additional methodologies for eradication, such as a possible vaccine, are available.

Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.


1. Dubey JP, Lindsay DS, Saville WJ, et al. A review of Sarcocystis neurona and equine protozoal myeloencephalitis. Vet Parasitol 2001;95:89-131.

2. Saville WJ, Reed SM, Morley PS, et al. Analysis of risk factors for the development of equine protozoal myeloencephalitis in horses. J Am Vet Med Assoc 2000;217:1174-1180.

Suggested Reading

  • Yeargen MR, Howe DK. Improved detection of equine antibodies against Sarcocystis neurona using polyvalent ELISAs based on the parasite SnSAG surface antigens. Vet Parasitol 2011;176(1):16-22.
  • Saville W, Reed S, Dubey JP. Prevention of equine protozoal myeloencephalitis. Presented at AAEP Annual Convention, Orlando, Fla., 2002. Updated 2011 and posted at http://www.aaep.org/health_articles_view.php?id=225.
  • MacKay RJ, Davis SW, Dubey JP. Equine protozoal myeloencephalitis. Compend Contin Educ Pract Vet 1992;14(10):1359-1367.
  • Saville WJ, Reed SM, Granstrom DE, et al. Response of horses exposed to Sarcocystis neurona when monitored biweekly, in Proceedings. 43rd Annual Am Assoc Equine Pract 1997;43:9.
  • Bello TR, Allen TM. An intensive approach in the treatment of clinical equine protozoal myeloencephalitis. J Equine Vet Sci 2008;28(8):479-483.


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