EPM in Horses 101: Causes, Symptoms and Recovery


It’s only three little letters. But EPM can cause a whole lot of fear in horse owners. EPM stands for Equine Protozoal Myleoencephalitis. This is a neurological disease which means it effects the horse’s coordination, spinal cord and brain. If left untreated horses can become paralyzed and die. EPM in horses is increasing in the United States, according to The Horse magazine.

Treatment needs to be started immediately for the horse to have any chance at surviving. The problem is that the early symptoms are the same as for many other medical conditions or even poor shoeing.

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What Is EPM in Horses?

EPM causes the horse to lose coordination and gradually become completely paralyzed. Early symptoms include:

  • Stumbling more than usual;
  • Falling for seemingly no reason;
  • Strange change in gait, often just on one side of the body;
  • Muscle loss on one side of the body;
  • Difficulty eating or dropping food constantly;
  • Strange head tilt;
  • One ear constantly droops while the other acts normally;
  • One eyelid droops while the other acts normally;
  • Muscles on one side of the mouth may seem to droop or become immobile;
  • Loss of balance to the point where the horse sways as if drunk while walking or leans against a wall or fence to keep from falling over.

Oddly enough, the usual vital signs like heart rate and temperature are rarely affected. If the horse is not treated in this time, the paralysis spreads to both sides of the body. The horse cannot eat or stand up. At this stage death is inevitable. The good news is that horses can recover if the disease is caught early enough.

What Causes EPM in Horses?

EPM in horses is caused by parasites. These parasites include:

  • Sarcocystis neurona: A protozoan (microscopic one-celled animal) which is the most common parasite that causes EPM in horses. It does this by attacking the animal’s central nervous system.
  • Neospora hughesi: Another protozoan that wreaks the same havoc as S. neurona.
  • Neospora canicum: Horses rarely get EPM from these protozoans. But it can does happen.

How do these microscopic parasites end up in a horse’s body?

  • They first live in animals like opossums, sea otters, skunks, raccoons, armadillos, cats and very rarely dogs.
  • The parasites enter these animals’ digestive systems and leave their bodies inside the animal’s bowel movements.
  • These contaminate the water, pasture or feed horses eat.
  • When a horse eats or drinks the contaminated food, the parasites travel from the horse’s digestive system into the central nervous system., including parts of the brain.
  • These invaders cause EPM.

Treatment Options Available for EPM in Horses

The first part of treatment is to get a positive diagnosis of EPM. This may take many tests to rule out other diseases like a brain tumor or equine wobbler syndrome. Unfortunately, there is no one simple test for EPM.

If a diagnosis is EPM, drugs are then administered. These include but are not limited to:

  • Paunzauril (brand name Marquis) is a paste that needs to be given for 28 days. The dosage is 5 mg per kilogram of the horse’s weight.
  • Diclazuril (brand name Protazil) is a pellet that includes alfalfa hay so the horse will eat it. It’s also given for 28 days. The dose is 1 mg per kilogram of the horse’s weight.
  • Sulfadiazine and pyrimethamine (brand name Re-Balance) is a liquid medication given for six months.
  • NSAID painkillers (NSAID stands for non-steroidal anti-inflammatory drugs).
  • Drugs to ramp up the horse’s natural immune system, called immunostimulators.

Some veterinarians may combine drugs considering the horse’s individual health. They may also recommend nutritional supplements like Vitamin E.

Sick horses cannot transmit EPM and therefore do not need to be quarantined. They do need clean bedding, clean water and feed to make sure they do not get even more parasites into their bodies.

Horses that recover from EPM are prone to getting more attacks throughout their lives. Horses that began treatment at the early stages have been known to recover enough to be ridden or even compete in horse sports or shows.

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Prevention of EPM in Horses

Preventing the parasites that cause EPM is the best way to prevent EPM in horses. However, this is easier said than done.

  • Possums are the most frequent carriers of the protozoans that cause EPM. Making sure possums cannot get into areas where horses eat and drink can be difficult to do. One way to prevent possums from being attracted to a barn or pasture is to clean up spilled food every day and to get rid of any roadkill or dead animals on the property. Easy access to food like carcasses, trash or spilled feed attracts many animals like skunks and possums.
  • Since horses become infected from contaminated water, avoid letting a horse drink from any natural water source like a stream or pond. It’s much easier to fence off a water source. This way, a horse cannot get to the water than it is to fence off small nimble animals like skunks and cats from water.
  • Horses can become infected with the dreaded parasites and yet never show any symptoms of EPM. This is thought to be due to the horse’s strong natural immunity due to proper diet, lack of stress and being kept clear of larger parasites like flies. Healthier horses are more likely to not get EPM while over-stressed, overworked, sickly horses will.
  • For reasons yet unknown, Warmbloods and older horses are most susceptible for getting EPM. Horses in the Southern states are also prone since more possums, armadillos and skunks live in that area.

To Sum It Up

EPM in horses can be lethal because it causes the horse’s whole body to become paralyzed. It is caused by parasites that live in the droppings of small mammals like cats, skunks and especially possums.

If caught early enough, horses can not only survive EPM but go back to work.

The images are from pixabay.com.

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