EPM and Your Horse

EPM is an equine disease that affects the central nervous system. EPM stands for Equine Protozoal Myeloencephalitis.

EPM causes horses to become unbalanced and weak. They may have facial paralysis and difficulty swallowing. If your horse is having neurological problems seek the advice of your veterinarian.

What Causes EPM?

EPM is caused by very tiny animals called protozoa. There scientific names are Sarcocystis neurona and Neospora hughesi. They are related to the organism which causes malaria in humans.

The protozoa need two hosts to live in and carry out their life cycle. A definitive host and an intermediary host. The horse is actually a dead end host.

The Virginia Opossum is the main definitive host for the protozoa and pass them out into the environment in their feces. The horse eats the feces and ingests the protozoa.

No most horses don’t deliberately eat possum poop! Typically this occurs in contaminated feed or from eating off the ground.

Other animals can be intermediate hosts including raccoons, skunks, domestic cats, and otters. The protozoa live and reproduce in their bodies but don’t cause them to get the disease. However, when the possum eats the infected animal as carrion then the cycle continues.

Public Domain, https://commons.wikimedia.org/w/index.php?curid=2346441
Life Cycle of S. neurona

What Happens When the Protozoa Gets Inside the Horse?

The parasite matures and may travel around the horses body. In a small percentage of horses this mature parasite reaches the central nervous system specifically the brain. Its unclear why some horses with protozoa present never develop the disease.

How Widespread is EPM?

EPM has been diagnosed world wide but is more common in the Americas. Not every horse that is exposed to the protozoa gets the disease. In fact, up to 90% of horses in certain locations may contain antibodies and do not have a clinical case of EPM.

Studies have shown that approximately 62% of EPM occur in horses younger than four years old, and 20% of cases were in horses older than eight years. Standardbreds, Tennessee Walking Horses, Thoroughbreds, Warmbloods, and Quarter Horses had the highest rates of cases.

How Do Vets Diagnose EPM?


  • Lameness
  • Depression
  • Facial paralysis
  • Difficulty swallowing or breathing
  • Stumbling – poor balance
  • Seizures

EPM can be difficult to diagnose. Horses display a variety of symptoms and no two animals respond the same.

Your veterinarian can do a blood test to look for anti-bodies to EPM. That means your horse has been exposed and has built up anti-bodies. Vets refer to this as being seropositive.

Can EPM be treated?

The FDA has approved several prescription drugs for the treatment of EPM. You will want to work with your vet to provide a medical treatment plan.

You vet may also recommend supportive treatments such as anti inflamatories or complimentary therapy such as PEMF.

We also recommend Excel products for supplementary Vitamin E.

While veterinarians can medically treat the disease your horse may have long lasting results. There is no vaccine available.

How Can I Prevent EPM?

  • Feed you horse from clean buckets
  • Don’t feed on the ground
  • Cover hay that may be exposed to wildlife
  • Use a hay rack
  • Keep rodents under control
  • Call a wildlife rehabilitator to learn how to humanely discourage possums.
  • Minimize stress levels especially when transporting or competing

How Do I Discourage Opossums Humanely?

The opossum is a valauble animal in the environment and does a lot of good. They eat numerous ticks and clean up dead carrion.

However, you may not want them in your barnyard.

Discourage opossums by not having food where they can get it. That means having tight fitting lids on your feed and trash containers. Also don’t leave out food for your barn cats or dogs. They possum will saunter right up and join them!

Feed your outside pets and remove the food dish as soon as they are finished.

Keeping the grass around the barnyard mowed will also help discourage them. They prefer brushes areas with cover.

Take Away

Take steps to make sure your barn and feed supplies are clean. That will go a long way to preventing EPM.

Have a question or would like a neurological exam for your horse? Give us a call at 859-472-4141

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