Horses and Equine Protozoal Myeloencephalitis (EPM)

Dr. Gray, if a horse is treated for a mild case of EPM, and the treatment is “successful”, can the horse make a full recovery or will it always be in their systems to where a possible recurrence could happen in the future. Thank you M.L.S.

Dear M.L.S.,

Equine Protozoal Myeloencephalitis (EPM) is a serious and potentially fatal neurologic disease of horses. It is also a disease near and dear to my heart, as two horses that I owned both developed it. My thoroughbred was treated, made a near 100% recovery, and hasn’t had a single relapse. My quarter horse/app was treated, did not quite recover his ability to canter, and relapsed so many times I lost count. So your question—full recovery or possible recurrence—is a good one.

According to Dr. Stephen Reed formerly of The Ohio State University College of Veterinary Medicine, the prognosis for horses with EPM seems to be similar regardless of the treatment used: 60 – 75% of horses improve on standard therapy. Unfortunately, less than 25% of affected horses return to their original function. While a number of medications have come on and off the market—and many continue to use the combination of trimethoprim/sulfa—there are currently only two FDA-approved medications for the treatment of EPM :Ponazuril (Marquis®) and Diclazuril (Protazil).

The main concern, however, is the percentage of horses that relapse days, weeks or even months after treatment. Exactly why horses relapse is unclear, but there are three possible reasons: 1) the parasite that causes the disease, Sarcocystis neurona, came out of a form of hibernation within the horse’s body, 2) a small but persistent focus of infection was never completely killed off, or 3) the horse was re-exposed to the parasite.

To ensure your horse’s chances for success, I recommend a three-pronged approach. First, in addition to prescription medication listed above, work with your veterinarian to determine if anti-inflammatories such as phenylbutazone (“bute”) or flunixin meglumine (“Banamine”) should be used, if antioxidants such as Vitamin E, Selenium and others might support nervous tissue, and if the B-vitamin folic acid may prevent the deficiency sometimes created with treatment. Also consider natural ingredients that support the immune system and a healthy inflammatory response such as Omega 3 fatty acids and MSM.

Second, continue treatment for as long as your veterinarian advises or until tests on CSF (cerebrospinal fluid) come back negative. With your veterinarian’s recommendation, include physical therapy such as massage, hand walking, and specific stretches or exercises designed to strengthen and support affected parts of the body.

Third, follow the currently recommended suggestions for preventing EPM in your horse, such as keeping the primary host (the opossum) off your property, minimizing contamination of feed, water and grazing areas from intermediate hosts (cats, raccoons, skunks and armadillos), and reducing stress in your horse.

Lydia F. Gray, DVM, MA SmartPak Staff Veterinarian and Medical Director Dr. Lydia Gray has earned a Bachelor of Science in agriculture, a Doctor of Veterinary Medicine (DVM), and a Master of Arts focusing on interpersonal and organizational communication. After “retiring” from private practice, she put her experience and education to work as the American Association of Equine Practitioner’s first-ever Director of Owner Education. Dr. Gray continues to provide health and nutrition information to horse owners through her position at SmartPak, through publication in more than a dozen general and trade publications, and through presentations around the country. She is the very proud owner of a Trakehner named Newman that she actively competes with in dressage and combined driving. In addition to memberships in the USDF and USEF, Dr. Gray is also a member of the Illinois Dressage and Combined Training Association (IDCTA). She is a USDF “L” Program Graduate and is currently working on her Bronze Medal. Find Dr. Gray on Google+

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36 comments on “Horses and Equine Protozoal Myeloencephalitis (EPM)
  1. Lauren says: I started a blog about my horse and her fight with EPM. I plan to document before, during and after treatments… including images and videos. <3

  2. Hannah says:

    I took in a horse last year with EPM. He couldn’t walk straight and fell down almost once a day. The vet said he had probably had it for years after doing the appropriate tests. We went the non-traditional route of using herbal medicine (Qing Hao San) and within a month he was walking better. 4 months of treatment and we retested him to find no traces of EPM. He is now back to running around the pasture, bucking, rolling and is even under saddle. We go through the appropriate tests every few months and so far, so good. We even went on a 7 mile trail ride a few weeks ago. Perhaps these alternative ‘medicines’ should be looked into and talked about more.

    • Eileen says:

      Interesting treatment Hannah. Do you have more information as to dosages, etc? And where do you get Qing Hao San? Thanks!

      • Jess says:

        I’ve also had success with the Qing Hao, it’s also happens to be inexpensive. You can get it through most holistic vetrinary centers.

    • BETTY OTT says:


    • rika says:

      Where can I buy the herbal medicine (Qing Hao San) .My Horse got a relapse dueto my vet who didn’t give him further medication.He was fine till I didn’t give him his meds anymore.

    • Jenna says:

      Has anyone found out where to get Qing Hao San?

    • Tawny says:

      I know your post on EPM treatment is old but I was hoping you could tell me where you got the Qing Hao San from? I have asked several vets about it and none of them have ever heard of it or were of any assistance in knowing where I could get some. Also what dose were you giving? Thank you, Tawny

  3. Claire says:

    My horse had epm. He was treated, and the vets said he made a full recovery, and 6 months after the all clear to go back to work he fell down again. My vet recommend I never ride him again for our safety and he’s been a permanent pasture pet since he was 9. I had my new vet look at him when he got his shots and she said he had no signs of neurological issues and he was perfectly fine(he’s 14 now). This new diagnosis confuses me, along with how come he fell after they said he was fine?

    • Nathalie says:

      EPM isn’t a disease that just goes away forever. In fact, most horses have already been exposed to the cause – the protazoa. Horses who have been diagnosed with EPM are subject to recurrences of this disease – so it may come and go. As the owner, you have to be totally in tune with your horse – what’s normal or not for him, particularly his gait. Horses with EPM are often recommended to never be ridden because you can never really know when you’re going to get them past the point of being neurologically sound. Remember, dead nerves never ever grow back; nerves around them try to take up the slack. So for your horse, if you see anything funky, retest him. A test from Florida costs 38 dollars to do. We just paid less than 200 dollars for our test, results, vet visit, and a coggins – things are better now. He probably fell because he had a relapse of EPM. Be sure to keep his immune system strong. vitamin E supplementation helps, as do immune supplements. smart-Pak has tons of them – very affordable.

      • Nathalie says:

        By the way, even though a veterinarian cannot necessarily recommend a horse be ridden again, with care and rehabilitation and very VERY special attention paid to warning signs of recurrent EPM, many horses are able to go back to productive riding. Some don’t, but in our case we were lucky. My cutting horse I will never really trust to work in cutting again in competition, but he can be ridden working cattle, some light cutting, etc.

  4. Cynthia R Skidmore says:

    i have had two horses with epm. the 1st had to be put down due to the disease progressed to seizures and unable to move hindquarters and blindness. i am now in my 2nd battle with the best horse i have ever had the priviledge to own. we are on our 3rd relapse since 10/11. trying to support him with vitamin e and microlactin. also have been doing at home rehab and chiropractic and massage therapy. would like to donate him to a program studying this horrible disease for research. any suggestions? thank you for your response.

    • Nathalie says:

      Where are you located? Are you near Florida? Have you talked to your veterinarian about donation? With what are you treating?

  5. Karen says:

    My horse was just diagnosed with EPM. My vet believes we caught it early so I’m hoping for the best. Currently she’s being treated with Oroquin-10 and 2 bute for the duration of the treatment. I’m now giving her some vitamin E and Selenium with her vitamins. Can you recommend any specific supplements, vitamins, etc that I should keep her on after the 10 day treatment is over? I want to do anything I can to keep her healthy.

  6. Katie says:

    My first show horse who is now 13 was diagnosed with EPM about three months ago, he is currently on Marquis and lots of different vitamins to help with his immune system. He has no sense of where his front right leg is and is constantly dragging it around. We do turn him out and so far he is fine but is there anything else you would suggest? He was on marquis for the first month then switched to another medication which made him worse so we then switched back.

    • SmartPak SmartPak says:

      Hi Katie, our first recommendation is to make sure you continue working with your vet to monitor your horse’s progress and condition. In addition to the medication your vet is prescribing, you may want to ask him or her about adding Vitamin E to your horse’s diet. Many veterinarians suggest horses undergoing treatment for EPM be supplemented with Vitamin E to support their muscle and nervous tissue. We’ve included a link to our Natural Vitamin E below. Best of luck!

      Natural Vitamin E:

      • Linda D Lightfoot says:

        Is EPM contagious from one horse to anothe

        • SmartPak SmartPak says:

          Hi Linda, thanks for asking! EPM is not transferred from one horse to another. The organism that causes EPM is a protozoa called Sarcocystis neurona, and horses can be exposed to it when they come into contact with opossum feces, often when grazing. If you’re looking for additional information about EPM, check out the EPM section of our Equine Health Library: – Dr. Lydia Gray

  7. Guy French says:

    I have a 3 year old bucking horse stallion that came down with EPM. He went down today and can get him back up but only for about 5 minutes. He has no clue where his hindend is. I’m starting him on Marquis tomorrow. He is eating and drinking great. What are his chances for survival?

  8. Joanna says:

    I have four rescues and I often donate money food and computers to a local rescue. I just found out Joey my paint I have got at Christmas from a rescue has EPM, early stages the meds are between 700-1000 and I just don’t have it. I normally do pretty well but its been a tough 2012. I was told sometimes rescues will help. Please help me save Joey.

    • Cheri Barker says:

      I have a 25 year old TB that relapsed after 60 days and 90 days on SMZs.

      She was then treated with Oroquin 10 and is doing well. The Oroquon 10 in less than $200 and is a 10 day treatment. It was easier on her body then the SMZs as well. Good luck and best wishes to you and Joey.

    • Cayln says:

      Ask your vet about payment options. Most of the time your vet will work with you on the bills, as long as you pay them some money each month they should be willing to help you out. I was $7000 in and quite a few wrong diagnoses before one of my vets figured out that it was EPM causing my horse’s problems. Trust me when I say they’ll work with you.

  9. We have a beautiful saddle horse mare that we believe to have EPM. We are a rescue taking care of anywhere from 25 to 35 horses at any given time. She, Rabbit, was an owner surrender and very malnourished when we got her. She has the classic symptoms of falling down (when she first came in), very weak hind end with difficulty standing for farrier. She was evaluated by a vet 3 months ago and he suggested getting her back to health and very light round pen work to see if we could build up her hind end. She is looking a lot better and she hasn’t fallen in over 4 to 5 months. However, her hind in still isn’t right. He did not recommend the test since it’s about $250 and he said it’s not 100% anyway. His recommendation is to let her be a pasture ornament and use the $500 to $700 Marquis treatment which is what he recommended for her to be used to save other horses. I have always treated our rescues as if they were my own. If Rabbit were mine, I wouldn’t hesitate to do the treatment. However, there are so many unknowns with EPM. My question is this, if we decide not to do the treatment, will she get progressively worse? I’m trying to research this but there doesn’t seem to be any clear cut answers. Any help and advice you can give us will be greatly appreciated. Right now, she has quality of life and euthanasia isn’t an option. I just worry about letting her be a pasture pet and what the new owner will be facing.

    • SmartPak SmartPak says:

      Kudos for rescuing what sounds like a wonderful horse! Unfortunately, if EPM is actually the cause of your mare’s weakness, the longer it is left untreated the more likely she is to develop permanent, irreversible damage to her nervous system, which may prevent her from ever being safely adopted out. While watching and waiting is appropriate in some situations, getting a diagnosis and knowing for sure what you are dealing with is a better way to go in other situations. Fingers crossed for you, Dr. Lydia Gray.

    • Karen Olek says:

      Started conventional treatment on my horse, he was so ‘out of it’, I decided to try natural. Website, ‘for the love of the horse’, ordered their Chinese herbs for the immune system and Neurological issues. CJ was on it about 3 weeks when we noticed a beginning of improvement. Right side muscles slowly returning. Left side was much worse, leg hind leg turned out, CJ didn’t know he had this leg, dragged it. Just this past week he is walking a little better on it, putting weight on it. There were some days he was so bad, it was heartbreaking. But I knew it would get worse when the parasites were being cleared, then better. I plan on using TTouch to rehab him.

  10. Debra says:

    I have a 28 year old gelding that has been on protazil for 3 weeks he started to act normal after about 13 days ,even trotted to the barn to get his feed. Now this past Monday he is back to walking sideways and leaning to one side ,could he be having a relapse while on the medication?

    • SmartPak SmartPak says:

      Thanks for sharing your experience. We strongly encourage you to contact your veterinarian as soon as possible about this latest development, so that he or she can adjust the treatment regimen if necessary. With a condition as serious as EPM, it’s important to keep the treating vet apprised right away of all changes, good or bad, so that the most appropriate program for healing is prescribed. We’ve got our fingers crossed for you! – Dr. Lydia Gray

  11. Tenley Keller says:

    What are your thoughts on doing a follow up with Oroquin-10 after the 28 day Marquis treatment? My horse just finsished his 28 days and we want to know what to do next.

    • SmartPak SmartPak says:

      Thanks for your question. Oroquin-10 is not currently FDA-approved, although horses have been reported to improve with this treatment. We recommend working with your veterinarian to develop a continued treatment, physical therapy, and follow-up plan. – Dr. Lydia Gray

  12. Lyndie Carter says:

    We have an 8 year old Tb stallion with rear limb ataxia (left worse than right). He falls frequently but is able to get up with great difficulty. Our vet saw him 4 days ago and drew blood to send off. I assume for a western blot, he then went to a conference. These symptoms have worsened since he saw him. He didn’t want to start txt with rebalance until the test comes back Wednesday, but the horse may soon not be able to stand. I don’t know if he’s so far gone that tx is futile? He’s deteriorated so fast but he still eats and drinks. We’re also giving him bute 2 gms per day. What is your opinion?

    • SmartPak SmartPak says:

      We’re so sorry to hear that your horse is not doing well. We were just at this very same equine veterinary conference, the AAEP Convention, and there were some excellent educational presentations on EPM. Hopefully your veterinarian will be in touch soon with some treatment advice from some of the best minds in the country! – Dr. Lydia Gray

  13. Mary says:

    I have a horse that was diagnosed with EPM by the walking and pulling the tail method. Other than being off balance while doing this (crossing his legs in the back), and sometimes cross-cantering, behind…he has not shown any other signs of EPM. We now have him on a 30 day course of Oroquin. I will start him on the above suggested Vitamin E, sillinium & MSM. Do you think there is a good chance my horse will return to normal functioning work?

    • SmartPak SmartPak says:

      Hi Mary, thank you for your question. EPM is unique in that it can impact every horse differently. The truth is that the horse’s prognosis is dependent on a variety of factors, all of which your horse’s veterinarian will be able to evaluate. Your best bet is to sit down with your veterinarian and discuss your horse’s unique situation and what your horse’s career might look like based on his medical history. – Dr. Lydia Gray

  14. Sue Davis says:

    Hi Dr. Gray, I have a 7 y.o. Irish T.B.. He got very grumpy, sour, and started tripping a lot, especially behind. He’d catch his toe and then the hind end would sort of collapse. At first I thought it was stifles and did the whole estrone thing, then had my vet XRay/evaluate and injected his hocks. He improved slightly and then started to decline again. I had him tested for Lyme (positive titer) and also did the blood test for EPM (worthless I now know) and of course he has been exposed (1:1000). I’ve been treating him with Doxy for about 3 weeks now and the tripping has improved 70%, but the canter is not what it used to be and he still catches behind some. The canter used to be like a rocking horse and now it feels disunited somewhat, worse to the left. We’ve done some neurological testing and he’s not bad – just a coulple of little things that could/could not mean something. I don’t feel like this is the athletic bouncing ball that I bought 7 months ago, but I don’t want to treat for EPM unwarranted. I know the spinal tap is the answer, but I don’t think I can do that without the hospital runnning up quite a bill with lameness evaluations/blocks/neuro exams first. It would be more cost effective to just treat him. It’s convoluted with the positive Lyme titer too. Suggestions, opinions, ideas? Thanks for your help.
    Best Regards,
    Sue Davis

  15. Dee says:

    Hi Dr Gray, I have a triple registered 9 yr old mare who has been off and on short stepping behind since I bought her. We thought she just needed her hocks injected due to a previous injury and the fact she had been shown all over the country, Top 5 Pinto World and Top 10 at Congress in showmanship. Had her hock injected, no change, tried Prevacox, no change, Bute some change, not consistent. In Sept 14 under saddle all of a sudden she could hardly carry weight. Called local vet thinking Chiro adjustment only to have her do a Neuro exam and blood tests, came back positive for EPM. Whoa…did 30 days of Rebalance had a 95% change in her gaits (better) decided to do another 30 days to be sure, meanwhile I had a second vet do a 2nd opinion. Had her retested only to find the Rebalance is not actually killing the Protozoa. Started her on Origon yesterday for 10 days with recheck in 6 weeks. The test indicates she hasn’t had the infection long. I talked to Dr Ellison who said I should be able to start her back under saddle at day 5and she should be greatly improved. Other then the short stepping behind have not had the major neurological issues so many have had, no falling down,etc but I’m just a little leary of riding her now, just in case. Any thoughts?

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