What is EPM in Horses

Last Updated on December 9, 2021

Ever heard of a horse getting EPM? Whenever I’ve heard that term thrown around, it’s always been in very serious tones and worried voices.  I knew that EPM in horses had something to do with a horse’s hind end starting to give out and that it could be very harmful.

But what really is EPM? What causes it? What does it do? Can it be stopped? Or can it be prevented? That is what I set out to discover in this article.  Turns out, the causes of EPM are more narrow than I thought, and there are ways to cure and prevent it!

So, thankfully, if a horse does contract EPM, they can be saved.  But, it’s important as a horse person to understand the disease, what it does, how it is contracted, what to do when it is contracted, and how to prevent it in the first place.  And that’s what I’ll be discussing in this article!

EPM in Horses: What is EPM?

EPM stands for Equine Protozoal Myeloencephalitis. It’s a “neurologic disease in horses caused by infection with the protozoan Sarcocystis Neurona (SN).  SN infects horses when they ingest the organism in contaminated feed or water,” according to the Iron Gate Equine Clinic.

So, it’s a disease horses get from digesting either contaminated food and water.  EPM typically causes horses to slowly experience neurologic dysfunctions, such as weakness in their hind legs and difficulty moving their legs with synchronization.

EPM in Horses: What is EPM?

Symptoms of EPM can have a slow onset or they can set in extremely quickly, depending on the case.  It’s very difficult to diagnose EPM by tools such as blood tests, and typically vets use the process of elimination to determine that the illness isn’t caused by another other than EPM what diagnosing a horse.

EPM in Horses: What Causes EPM?

Why do horses get EPM? So, we said that horses get EPM from the digestion of contaminated food or water supplies and that this infection comes from Sarcocystis Neurona.  But what is that? Essentially, it operates kind of like a bacteria, carried from one organism to the next.

In this case, Sarcocystis Neurona is predominantly carried by opossums, which passes the “bacteria” through its feces.  Opossums live outside, and so do horses. So, it’s possible that horses could come into contact with opossum feces during their turn out. 

If a horse ingests feces of an opossum, or food or water contaminated with the feces of an opossum, carrying Sarcocystis Neurona, then this horse could contract EPM.  

While Opposums can transfer Sarcocystis Neurona from one to the next, a horse that gets it is considered a “dead-end host.” This essentially means that the horse cannot pass the “bacteria” along any further; animals and people that have contact with an infected horse will not have the Sarcocystis Neurona passed on to them.

What Can You Do for a Horse that Has EPM?

When I first started writing this article, I was under the impression that EPM was a fatal diagnosis;  I had heard of many senior horses getting it and not being able to bounce back from it.

EPM in Horses Treatment

But, thankfully, I was wrong! There are a few different methods of treating EPM in horses.  First, there’s the obvious use of phenylbutazone (commonly called “bute”), to help with reducing pain and inflammation.  Think of this like Advil for horses. Bute is used in horses to help with many different ailments and illnesses.

Similarly, infected horses can also be treated with Banamine, which operates somewhat similarly to Bute.  While these medicines will help take the edge off, so to speak, they won’t get rid of the EPM altogether.

To do this, frequently an oral paste is prescribed.  Ponazuril Marquis is typically this paste, and it is prescribed for a 28-day period.  Sometimes, vets will prescribe the infected horse with some kind of antibiotics, to initially help with the infection, while waiting for the prescription to arrive.

EPM in Horses: Supplements

Then, in supplement, some vets recommend the use of Vitamin E tablets or powders.  These are more of an afterthought after the prescribed medicines are used. Vitamin E is high in antioxidants, and it can assist the horse’s system in cleansing itself from the “bacteria.”

But how successful are these treatments?  According to Iron Gate Equine Clinic, half of the infected horses that are properly treated will return to the way they were before the infection.  The other half will still improve but will have some lasting physical issues.

Typically, the horses that only offer mild signs of EPM when treated will be the ones that are fully returned to the way they were before.   And, the horses with more severe symptoms are likely to be the ones that have some lasting physical issues.

But, some treatment is better than no treatment.  Left untreated, EPM can cause such severe hind-end weakness in horses that they will no longer be able to stand.  Even in the most severe cases, if EPM is treated properly, a horse could at least become well enough to live out its life in retirement.

Preventing EPM

Due to the fact that horses contract EPM from a “bacteria” carried by opossums, the best prevention from EPM is to try to limit your horse’s exposure to opossums.  

So, if your area is known for having opossums, set live traps, and keep an eye on areas that are likely to draw in animals; any warm or covered area.  Check hay bales for feces before you feed them, and try to make sure that your water and feed supply are protected.

Preventing EPM


EPM can be deadly if left untreated, but thankfully, it is a treatable condition! If you fear that your horse might have EPM, don’t hesitate to call your vet.  As you read, the sooner symptoms are recognized and treated, the more likely your horse is to make a full recovery.

I hope this article helped you learn more about EPM, the causes, treatments, and prevention of it.  I know it definitely helped me be better informed about how to best protect my horses!

If you found this article helpful, please share it, and share with us your experiences dealing with EPM!


How long does it take for a horse to show signs of EPM?

Equine Protozoal Myeloencephalitis (EPM) in horses is caused by protozoan parasites that are picked up from soil, water or plants that are contaminated with the parasite's eggs. Horses usually become infected by swallowing contaminated water or ingesting contaminated foodstuffs such as grass, hay and grain.
The incubation period of EPM varies depending on the severity of the infection. Normally it takes about 3 weeks for the first signs of EPM to appear. However, horses can show symptoms of EPM within 3 days of infection if they have a severe infection. If the horse has a light infection, it could take few months for symptoms to show up.

Is EPM in horses curable?

To date, there is no cure for Equine protozoal myeloencephalitis (EPM) disease, but the condition can be managed.
There are some treatments available for EPM in horses which aim to ease the symptoms and improve the quality of life of horses with this condition. These treatments are not designed to cure the horse completely, but they are helpful in managing this disease better. Some of these treatments are designed to relieve pain and discomfort caused by EPM in horses, while others are used to treat other conditions that may occur concurrently with EPM or as a result of it.
The treatment time for EPM in horses varies depending on the severity of the infection. The most common treatment methods involve antibiotics, anti-inflammatory drugs and supportive care. Some cases of EPM require more intensive supportive care like respiratory assistance or intravenous fluids; these treatments are very expensive and lengthy.

Should you exercise a horse with EPM?

Exercising a horse with EPM has proven benefits that outweigh the risks associated with it. Physical activity helps build muscles and reduces stress levels in horses. It also improves cardiovascular health and reduces joint stiffness in older horses.
Horses with EPM should not do any strenuous exercise as it may put too much stress on their heart muscle. However, light or moderate exercise is okay as long as they don't overdo it. Exercise should be done with care to prevent further injury or pain in the horse.

Is there a vaccine for EPM in horses?

The Equine Protozoal Myelitis (EPM) vaccine is an immunisation for horses, which is given to horses to prevent the disease. The vaccine helps the body to develop immunity against this virus.
There are two types of EPM vaccines approved by USDA: an inactivated virus vaccine and a live attenuated (weakened) virus vaccine.
Inactivated virus vaccines work by introducing killed virus particles into the body. It is usually considered safer than live attenuated vaccines, as no live active viruses are present and it cannot cause the disease it is designed to prevent.
The live vaccine is a more potent form of a vaccine because it contains a weakened form of the virus. A live virus needs to replicate in order to be effective so it can stimulate an immune response from the horse's body. By injecting a live vaccine, the immune system can better prepare for a real-life attack of the disease. Normally the weakened form of the virus is enough to stimulate an immune response but not enough to cause illness.
The administration of both vaccines should be done under veterinary supervision.