EPM Risk

EPM is a serious and sometimes fatal neurological disease of horses. Almost every part of the country has reported cases of EPM, although the incidence of disease is much lower in the western United States especially in regions with small opossum populations. Studies show that in states where the opossum is present, up to 53% of the horse population can be exposed to the parasite.¹ Due to the transport of horses and feedstuffs from one part of the country to another, however, almost all horses are at risk.

Not all horses that are exposed to the protozoan Sarcocystis neurona will develop the disease and show clinical signs of EPM. Some horses seem to mount an effective immune response and are able to combat the disease before it gains a foothold. Other horses, especially those under stress, can succumb rapidly to the debilitating effects of EPM. Still others may harbor the organisms for months or years and then slowly or suddenly develop symptoms.

A study conducted at The Ohio State University has identified several risk factors:²

• Age - those animals that are 1 - 5 years of age and older than 13 years are at risk
• Time of year - more infections are seen in the spring and summer
• Type of surrounding landscape - those farms with woods and therefore opossums were at higher risk
• Level of Training - those horses in heavy training that are traveling to shows or races are more likely to be affected
• Prevalence of EPM – Horses residing on premises where EPM was previously diagnosed had an increased risk for developing EPM

Learn More: What can be done to prevent EPM?

The safety of Marquis^® with concomitant therapies in horses has not been evaluated.

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¹ Saville WJ, Reed SM, Granstrom DE, et al, Seroprevalence of antibodies to Sarcocystis neurona in horses residing in Ohio. J Am Vet Med Assoc 1997; 210:519-524.

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.