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.
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 onazuril (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.