What is EPM?

Equine Protozoal Myeloencephalitis (EPM), is a disease that affects the central nervous system of a horse. This disease is commonly seen throughout the United States, primarily in areas populated with opossums and other woodland creatures.

What Causes EPM in Horses?


The primary cause of Equine Protozoal Myeloencephalitis is the single-celled, parasitic, protozoan, Sarcocystis neurona. 

Through a complicated life cycle, these protozoa eventually reside in the infected horse’s central nervous system. More so, they cause inflammation in the brain stem or spinal cord, creating the condition referred to as myeloencephalitis.

Additionally, Sarcocystis neurona breaks down into a two-part cycle which includes a definitive host and several possible intermediate hosts.

Generally, the host is an infected opossum, who sheds an infective form of the parasite, S. neurona in its feces. The horse then ingests the opossum feces, along with the ineffective form of the parasite, defined as the “sporocyst."

After ingested, the parasite continues to the reproductive phase within the horse. Eventually, a form of the parasite morphs into a new stage called “merozoites”.

Finally, the merozoites reach and damage the central nervous system, leading to neurologic symptoms and weakened body condition.

Meanwhile, the intermediate host is an animal that does not spread an infective form of S. neurona. Instead, this host carries the parasite so that it can complete its life cycle. An example of these hosts include; skunks, armadillos, raccoons, cats, and even sea otters.

Signs and Symptoms of EPM in Horses.


The American Association of Equine Practitioners defined the main symptoms of Equine Protozoal Myeloencephalitis as Asymmetry, Ataxia and Atrophy.

  • Asymmetry describes a symptom that is worse on one side of the body than the other. This is most often seen in muscle development and distribution.

  • Ataxia describes the horse's lack of coordination. A head tilt, intermittent lameness, and poor balance are common examples.

  • Atrophy describes muscle decay and atrophy. Horses with a positive diagnosis can suffer severe muscle changes.


Being a disease of the CNS, the brain and the spinal cord become affected. Moreover, the clinical signs and severity of this disease to vary. It is more common for the signs of disease to associate with spinal cord damage. However, we also see evidence of damage in the brain.

EPM Chart

Clinical Symptoms of EPM.


Because the progression of the disease varies, different clinical signs of EPM horses range in severity. Some common clinical symptoms and signs are:

  • An abnormal gait

  • Intermittent lameness

  • Muscle atrophy

  • Loss of sensation in the face, neck, or body

  • Head tilt

  • Paralysis of the muscles of the eyes, face or mouth

  • Poor balance

  • Major changes in mood

  • Weakened immune response

  • Difficulty swallowing


The most severe symptoms in horses include seizures, collapsing, and the inability to stand.

If you suspect symptoms in your horse, notify your vet immediately. Some of these signs could be part of a multiple neurologic disorder which requires further diagnostic testing.

How are Horses Infected with EPM?


After ingesting the infective protozoa, a horse can have additional risks to develop this disease.

The first and greatest risk factor, is a weak immune system. When looking at disease progression, horses prone to autoimmune diseases and weakened immune system cells are at high risk.

In addition, the equine immune system can be seriously compromised during times of stress. Even the healthiest animal can experience high stress situations that leave them more susceptible to infections and disease.

Some examples of stress include heavy training, traveling long distances, and experiencing environmental changes, just to name a few. It is important to note if your horse is experiencing a weakened immune system from these stress factors and act accordingly.

Next, a risk factor is the lifestyle and life stage of your equine. If you are traveling from competition to competition, you are risking your animals exposure to multiple parasites and bacteria. Moreover, if your horse is older in age, they most likely have a harder time fighting infection.

Not to mention, another significant risk factor is geography. This directly relates to horses residing where opossums are commonly found, making risk factors highly prevalent.

These multiple risk factors can directly affect the development and course of this neurologic disease in an infected equine.

How is EPM Diagnosed?


Your vet can run tests on two different sample types: blood anti-body test and cerebrospinal fluid CSF. Even though there is not a definitive test, blood titers will give you a good idea of exposure to possible infection. A positive titer in the spinal tap of cerebrospinal fluid is more indicative of infection versus exposure.

Because the diagnosis process for this disease is incredibly difficult, research laboratories are dedicated to discovering knew techniques. For example, UC Davis is expanding their knowledge of Equine Infectious Disease's and how to further develop diagnostic testing.

How to Treat EPM in Horses.


In the occurrence of a diagnosis, your vet can prescribe medications to help combat it. However, treatments can be extremely expensive and taxing on your animals health.

Treatment times are long and can last from one month to several months. The administration of supportive FDA approved medications like NSAIDs can help to decrease the inflammation created during protozoa die-off.

At Excel Supplements, we are happy to be able to complement medical treatment for symptoms with ExcelEQ ProElite™.

Our ProElite™ formula overflows with natural vitamin E antioxidants, polyphenols, and a blend of plant-based Omegas. This aids in keeping an infected horse’s hindgut ability to absorb vitamins and nutrients at full capacity.

Protection against free radicals released during protozoa kill-off is of high importance. So, omega-3 and vitamin E feed additions are a great compliment during treatment and beyond. It is imperative that these horses receive the best possible medical attention and nutritional support to lead to the best outcome.

Can You Prevent EPM?


The best way to prevent exposure to this disease is to keep food and water areas clean of feces. Again, these feces could contain the protozoa responsible for exposing your horse. It is crucial to keep debris clean from high traffic areas at all times to prevent this disease.

In addition, feed your horse a well-balanced diet with trusted ingredients and processing procedures.

Remember, all horses are at risk to this disease. Regular check-ups with your vet are recommended to stay on top of your equines overall wellness.
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