EPM: Cause, Symptoms, and Treatments

Seven years ago, my gelding, Hershey, suddenly came up lame.   The lameness was so unusual though that I couldn’t determine the source of it.  It didn’t appear to be in any one leg or hoof, but more of a problem in the spine or neck and it was only noticeable when he was under saddle.  Like most of us would do, I took him to my vet right away.

It was a cool and rainy day when I unloaded him at the vet’s office and Hershey was shivering after the trailer ride.  My vet immediately suspected EPM (Equine Protozoal Myeloencephalitis) and wanted to test him for it.  I had heard of EPM at the time, but didn’t know too much about it.  You can bet I did some research, though as I waited for the test results to come back (which seemed to take several weeks if I remember correctly).

The blood serum test came back negative and I breathed a big sigh of relief.  But I still had no clue of what was wrong with Hershey . . . so we were off to another vet, and then another, and then another. . .

I never did get a definitive diagnosis on Hershey, and the lameness still exists today, but it’s still only noticeable when he’s under saddle.  Other than that, he’s very healthy.

I’m thankful that Hershey didn’t have EPM, but many horses aren’t so fortunate.  EPM is the most commonly diagnosed (and misdiagnosed) neurological condition today.

EPM is a tricky diagnosis since it often mimics other conditions and has a wide range of symptoms that can affect multiple parts of the horse’s body.  To make matters worse, the diagnostic tests can also produce false negatives (or positives) and the only definitive way to diagnose the condition is through post-mortem examination.

With that said though, the best way to diagnose EPM is through ruling out other possible diseases, neurological examination, and laboratory tests.

Other diseases/conditions that can mimic EPM (and should first be ruled out) include:

  • Wobblers;
  • Rabies
  • Eastern or Western Equine Encephalitis;
  • Equine Herpes Virus 1;
  • Lyme Disease;
  • West Nile Virus;
  • Cushing’s disease;
  • Selenium deficiency or toxicity; and
  • Other lameness issues.


Causes of EPM

EPM is caused by a protozoa–usually Sarcocystis neurona and more rarely by Neospora hughesi which is carried by opossums which obtain the protozoa by feeding on cat, raccoon, skunk, or armadillo carcasses (intermediate hosts).

epm diagram

The protozoa is transmitted to the horse when he consumes forage, feed, or water that has been contaminated by opossum feces containing  the infective sporocysts of the disease.

Once the sporocysts have entered the horse’s digestive system, they move into the bloodstream and cross the blood/brain barrier.  They then begin to attack the central nervous system of the horse causing one or several of many possible symptoms.

It’s been estimated that as many as 50% of horses have been exposed to the sporocysts that cause EPM, but only a very small percentage actually develop the disease.  Immune function seems to play a critical role in the development of the disease and horses with weakened immune systems are at a higher risk of developing EPM.

In doing this research, I came across several articles, including  this one by holistic veternarian, Dr. Gerald Wessner, which gave a little different view of EPM.  Dr. Wessner believes the reason we have seen so many EPM cases in recent years is not because opossums are on a rampage, but because horses’ immune systems are being overburdened by vaccines, dewormers, antibiotics, NSAID’s, etc.  I don’t know about you, but I think this makes quite a bit of sense. . .


Symptoms of EPM

As I stated before, the symptoms of EPM can vary widely and can range from mild to severe.  The following are a list of possible symptoms affecting the head:

  • droopy lip;
  • facial twitch;
  • dropping feed;
  • trouble swallowing;
  • head tilt; and
  • drooping ear.

Symptoms that can appear in the body include:

  • Uncoordinated movement of the rear feet, worse on one side;
  • Lameness that comes and go, often switching sides;
  • Changes to any gait;
  • Lethargy;
  • Hind end weakness;
  • Problems balancing when a hoof is lifted;
  • Circling, slipping, or falling while walking;
  • Muscle atrophy, often over the rump or shoulders;
  • Leaning on a stall wall for balance;
  • Dragging a hoof, especially while turning;
  • Sore back;
  • Unusual sweating patterns; and
  • Carrying the tail to one side, or away from the body


Treating EPM

Once EPM has been diagnosed, treatment should be started immediately.  The sooner the condition is treated, the more likely the chance of recovery.  If left untreated, EPM can result in permanent damage to the central nervous system and possibly death.

There are currently three FDA-approved conventional treatments for EPM which are said to have a 60-70% success rate.  They include:

  • Ponzauril (marketed as Marquis);
  • Diclazuril (marketed as Protazil); and
  • Sulfadiazine and pyrimethamine (marketed as Re-Balance).

These drugs do not kill 100% of the protozoa, but reduce the numbers enough so that hopefully the horse’s immune system can take care of the rest.


Alternative Treatments

I am not suggesting that anyone attempt to diagnose and treat EPM on their own without veterinary advice.   But if your horse has been diagnosed with EPM and you are of the mindset that more chemicals are not the answer, I’d like to share some alternative treatment options with you.  Here are a few:

  • Homeopathy, such as this kit from Earth Song Ranch;
  • Chinese Herbal Blends such as this one from For the Love of the Horse;
  • Western Herbal Blends such as this one from Effective Pet Wellness;
  • Nutritional therapy such as Vita Royal’s EPS Formula.

Some other alternative EPM treatments (usually performed by holistic vets) include:

  • Acupuncture/ acupressure; and
  • Autogenous vaccination (injecting horse with his own blood at specific acu-points).


Immune Support

Regardless of the EPM treatment you choose for your horse, immune system support is vital both during and after treatment.  Without it, relapses are common.

The best way to support the immune system is a natural diet of primarily grass forage (fed at 2-3% of the horse’s body weight).  Eliminating grains and processed feeds as much as possible is beneficial.  Here are some other ways to provide immune support:

  • Supplemental vitamin E and other antioxidants;
  • Herbs such as Astragalus, Siberian Ginseng (an adaptogen), Feverfew, Nettle, Yarrow, Cleavers, Dandelion Leaf, Calendula, Boneset, or Pau d’arco;
  • Regular acupuncture, acupressure, and/or massage sessions;
  • Limiting the number of vaccines, dewormers, and other chemicals your horse receives; and
  • Stress reduction (allowing horse to live with other horses, limited hauling, etc.).


I know this has been a lengthy post, but I hope it will be beneficial to at least some of you.  Remember that you have choices when it comes to your horse’s health care, especially where EPM is concerned.  And you shouldn’t be afraid to do what you feel is best for your horse.





Equine Protozoal Myeloencephalitis

Equine Protozoal Myeloencephalitis (EPM) by Jessica Lynn

Equine Protozoal Myeloencephalitis (EPM) Testing by the College of Veterinary Medicine at Cornell University

EPM: Elusive, Pernicious, Manageable

EPM Testing, Treatment Options Reviewed

EPM and Herbs

EPM by the American Quarter Horse Racing Journal

Equine Protozoal Myeloencephalitis (EPM) by Veterinary Institute of Integrative Medicine

EPM Recovery at Its Best: Great News for EPM Horses


Hi! My name is Casie Bazay. I'm a mom, a freelance writer, and a certified equine acupressure practitioner.

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4 Responses

  1. Kaite says:

    My mare had a spontaneous, severe attack of the devastating neurological disease EPM (equine Protozoal Myeloencephalitis) in February of this year. She couldn’t stand, frequently fell over due to the Protozoa taking over her nerves. We got her to the clinic less than an hour after the first signs, She spent 6 days in the vet clinic. In that time, her EPM test came back positive and we began treating her with Marquis. When she came home, it took 3 people to get her the 25′ to her new stall. We also began using the EPM kit from effectivepetwellness.com (herbal) that goes in and breaks open the Insisted cells so the Marquis could do its job better. We also put her on Pau D’arco which does the same thing. Along with the Silver Lining products (brain and nerve support, herbal dewormer, LCR and immune support). Less than one week from getting her back home, I began doing short walks maybe 2 minutes long. Any depression or hill we went up/down, dyzzi became very unsteady and would almost fall. She was very picky with her feed, she would only eat alfalfa (what she was on before she got sick) so we had to give her a little bit at a time. Day 9 of her being on Marquis, I had my chiropractor come out and adjust her (dr Deb O’rielly)
    Week 7 I was riding her at the walk. Week 9 I was able to lope for very short periods.
    Week 10 she was retested and CAME BACK NEGATIVE. The vets retested her 4 times, against her first sample and to the new one and the current one came back negative every time!!! No chance of relapse.
    I’m at week 20 today. So far we have been back to competitively team sorting and working cattle, jumping small jumps, sliding stops and spins, trail riding in the Colorado mountains, and is 100% sound.
    I know not all stories are like mine, but there is hope for the EPM horse. Positivity and hard work coupled with love and herbs and Marquis is what made my little miracle pony what she is today 100% recovered and Better than before.

    • Casie says:

      Hi Kaite–thanks for sharing your mare’s story. It’s good to hear that such a serious case made a complete turnaround! Sounds like you did everything within your power to help her. Kudos to you and happy trails. 🙂

  2. My horse was diagnosed with EPM by a chiropractic vet. I had a gut feeling she was off and took him to another vet 50 miles away. He felt that was not a correct diagnosis either and started asking about my bit. His symptoms were chronic head tossing and stumbling. He told me the bit I used looked like it could pinch his tongue next to the small roller (Mylar HBT MB04) and that his mouth and tongue size didn’t match the bit. He said that he might be stumbling because he was stressing more about the bit and not watching where he was going, or that I needed to build up his hindquarter muscles. I started doing rollbacks and found a bit with more tongue relief and all symptoms stopped. He is fine now and that has been over a year.

    • Casie says:

      Hi Jeannine–yes, there are so many things that could look like EPM (just like with my horse). I have a head tosser as well and realized that it was due to TMJ issues. Always good to get a second (or third or fourth. . .) opinion if you don’t feel right about things though.

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