Equine Protozoal Myeloencephalitis (EPM) in Horses

Share:

Favorite
Please login to bookmarkClose
Please login

No account yet? Register

Fact Sheet: EPMEquine protozoal myeloencephalitis, or EPM, in horses was first recognized in the mid- to late-1960s as a “segmental myelitis.” It wasn’t until 1974 that scientists identified a single-celled parasite that prompted the name change to equine protozoal myeloencephalitis. Veterinarians now know two parasites, Sarcocystis neurona or Neospora hughesi, can cause EPM, but most cases are caused by S. neurona.

Opossums are the definitive hosts for S. neurona. They become infected by scavenging on intermediate hosts (skunks, cats, raccoons, armadillos) with S. neurona sarcocysts—walled-off “pockets” containing the infectious form of the parasite, which has reproduced here asexually—in their muscles. Once ingested, mature sarcocysts release bradyzoites, which transform and reproduce sexually in the small intestine, producing oocytes. The opossum sheds fully sporulated oocysts or sporocysts in its feces. They contaminate the environment and infect intermediate hosts when consumed.

Horses are incidental hosts that become infected by consuming the sporocysts in the environment. Unlike intermediate hosts, horses—as incidental or aberrant intermediate hosts—do not serve as reservoirs for infecting opossums (i.e., sarcocysts do not form that opossums later consume) and do not spread S. neurona directly to other horses.

Horses with EPM typically show signs consistent with spinal cord injury, such as ataxia (incoordination), gait abnormalities that can mimic lameness, and
muscle weakness and/or atrophy. Less commonly, they exhibit cranial nerve deficits manifesting as dysphagia (difficulty swallowing, abnormal airway function) or abnormal behavior and state of consciousness or even seizures. Affected horses typically experience asymmetric neurologic deficits and focal muscle atrophy. Signs can come on acutely or have an insidious onset.

Learn more helpful, research-supported information about equine protozoal myeloencephalitis in horses in this fact sheet.

Share
Favorite
Please login to bookmarkClose
Please login

No account yet? Register

Written by:

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she’s worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

Related Articles

GettyImages-138157016-scaled
Seasonal Manure Changes
Why is Your Horse Roaring and Whistling?
BEVA Provides Information on Medicine for Horse Owners

Stay on top of the most recent Horse Health news with

FREE weekly newsletters from TheHorse.com

Weekly Poll

sponsored by:

How frequently do you schedule dental wellness checks with your veterinarian?
152 votes · 152 answers

Readers' Most Popular

Sign In

Don’t have an account? Register for a FREE account here.

Need to update your account?

You need to be logged in to fill out this form

Create a free account with TheHorse.com!