EPM (Equine Protozoal Myeloencephalitis)By: Dr. Lydia Gray
Equine Protozoal Myeloencephalitis (EPM) is a disease of the central nervous system (brain and spinal cord) caused by the protozoa Sarcocystis neurona. EPM is transmitted by the opossum through intermediate hosts, also known as carriers, which may include birds, cats and other animals.
EPM is characterized by:
- Ataxia (incoordination)
- Asymmetry (worse on one side of the body than the other)
- Atrophy (loss of muscle mass)
Many veterinarians suggest horses undergoing treatment for EPM be supplemented with Vitamin E to support their muscle and nervous tissue. Other antioxidants as well as natural anti-inflammatories such as MSM, Omega 3 Fatty Acids and certain herbs may be beneficial in reducing damage to cells as the protozoa are destroyed.
In addition to a complete physical examination, your veterinarian will perform a series of specific neurological tests such as crossing legs, pulling the tail, blindfolding, etc. Because there are many conditions that can cause neurological signs, additional tests such as x-rays, bloodwork and spinal tap may be required to rule out things like “wobblers disease” or herpes virus.
There are currently three FDA-approved medications on the market to treat EPM: Marquis® (ponazuril), Navigator® (nitazoxanide) and ReBalance™ (sulfadiazine and pyrimethamine). A fourth product, Protazil (diclazuril) has been approved by the FDA but is not yet on the market.
In addition, some veterinarians recommend the prescription medications bute (phenylbutazone), Banamine® (flunixin meglumine) or Prednis Tabs® (a corticosteroid) as anti-inflammatories, to help manage pain during treatment.
Since the opossum is the definitive host of the protozoa that causes EPM, and birds, cats and other animals are carriers, measures to keep these animals away from your horses’ food and water sources may reduce the risk of infection.
- Will my horse relapse?
- Should I use one of the prescription products as a preventative?
- Are the other horses in the barn likely to develop EPM?
Further Reading for You
From the SmartPak Ask the Vet Blog:
From The Horse Journal:
- Battling EPM: Choose your weapons, March 2005
- EPM Continues to Defy Logic, February 2001
- EPM in Horses, August 2007
- EPM is Becoming a Catch-All Diagnosis, December 2002
- Is an EPM Cure Realistic? August 2004
Further Reading for Your Veterinarian
Mackay RJ, Tanhauser ST, Gillis KD, et al. Effect of intermittent oral administration of ponazuril on experimental Sarcocystis neurona infection of horses. Am J Vet Res. 2008 Mar;69(3):396-402.
Cohen ND, Mackay RJ, Toby E, et al. A multicenter case-control study of risk factors for equine protozoal myeloencephalitis. J Am Vet Med Assoc. 2007 Dec 15;231(12):1857-1863.
Duarte PC, Ebel Ed, Traub-Dargatz J, et al. Indirect fluorescent antibody testing of cerebrospinal fluid for diagnosis of equine protozoal myeloencephalitis. Am J Vet Res. 2006 May;67(5):869-876.