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Diagnosis Prior to Treatment Critical to EPM Recovery



MERCK Animal Health

MERCK Animal Health

Merck Animal Health and expert veterinarians agree diagnosing EPM can be difficult, but is money and time well-spent.

Equine Protozoal Myeloencephalitis (EPM) is one of the most feared diseases among horse owners. So feared, that owners might be tempted to request their veterinarian treat their horse for EPM without proper diagnostic measures. While early treatment is critical to stopping the disease from causing further nerve damage, if the horse does not have EPM an EPM treatment product will not be effective.

Amy Johnson, D.V.M., Dipl. ACVIM, assistant professor of large animal medicine and neurology at the New Bolton Center at the University of Pennsylvania, says treating EPM without a diagnosis can cost owners money and time.

“Many diseases can cause signs similar to EPM, but will not respond to EPM treatment. If the horse is treated for EPM, but actually has another disease, the owners have not only wasted their money, but also time that could have been better used pursuing the true cause of the horse’s problem,” Dr. Johnson says.

Stephen Reed, D.V.M., Dipl. ACVIM, internal medicine veterinarian at Rood and Riddle Equine Hospital in Lexington, Ky., agrees with Dr. Johnson.

“Signs of EPM can vary from neurologic to a mysterious lameness, so a thorough diagnostic work-up is really critical to make sure we are treating the horse appropriately and thus, improving his chances of recovering,” Dr. Reed says.

Diagnosis can be difficult, but should be done

Diagnosing EPM in a living horse can be tricky because the clinical signs are variable, but it is time and money well spent.

“The best way we know to diagnose EPM in a living horse is the combination of a thorough neurologic exam, antibody testing and appropriate diagnostic testing to rule out other diseases that can also cause neurologic signs,” Dr. Johnson says.

There are several diseases that cause neurologic signs in the horse similar to EPM, but all are treated differently.

“West Nile virus, rabies, tetanus, wobbler syndrome, eastern and western equine encephalitis and equine herpes myeloencephalopathy (EHM), and even trauma can all cause neurologic deficits in horses,” Wendy Vaala, V.M.D., Dipl. ACVIM, Merck Animal Heath equine technical services veterinarian says. “Without thoroughly evaluating the horse and performing appropriate diagnostic tests, we can’t effectively treat them.”

“Currently, the recommendation for antibody testing is to collect spinal fluid and blood samples and compare the antibody titers in each to determine if there is evidence of a central nervous system infection. If spinal fluid is not feasible, it is reasonable to only collect a blood sample,” Dr. Johnson says.

Treatment options

If your veterinarian confirms your horse has EPM, there are fortunately FDA-approved EPM treatment products available. One option is PROTAZIL® (1.56% diclazuril). PROTAZIL is the only FDA-approved product that comes in a convenient top-dress formula.

“Having your horse diagnosed with EPM is stressful and having to treat them for 28 days or more with an oral paste is not always easy for the owner or the horse,” Dr. Vaala says. “The alfalfa-based PROTAZIL pellets are well-accepted by horses and consumed without the mess, fuss and stress of a paste.”

Greggory S. Bell, D.V.M., from Centennial Equine Sports Medicine in Pagosa Springs, Colo., says his clients have appreciated PROTAZIL’s ease of administration.

“We have been using PROTAZIL in our practice with excellent results,” Dr. Bell says. “Our clients find the pellets much easier to administer than a paste. And, the horses like it better as well. We’ve even seen some horses eat the PROTAZIL pellets before consuming their grain concentrate. As a result, we’ve been able to achieve better treatment results against this devastating disease.”

Equally as important as the product’s palatability and easy administration is its ability to quickly reach therapeutic levels without the need for a loading dose at the start of treatment1.

“When it comes to treating horses with EPM, using a product that is rapidly absorbed means the damaging parasite has less time to attack the horse’s nervous system. PROTAZIL quickly attains effective drug levels against a disease where time matters,” Dr. Vaala says.

Daniel Yates, D.V.M., an equine practitioner in Wilmington, Ohio, says he relies on PROTAZIL to treat the EPM cases he sees in his practice.

“EPM is a serious disease threat in Ohio. The PROTAZIL treatment regimen achieves therapeutic levels quickly and without a loading dose. I’ve used PROTAZIL to treat my own horses, as well as my clients’ horses. PROTAZIL is easy to use, horses find the pellets palatable and the product is priced competitively,” Dr. Yates says.

Disease prevention

Although the veterinary community is constantly working toward a proven way to prevent EPM, for now, the best way to keep your horse from getting the disease is to avoid exposing him to opossum feces.

“Maintaining a clean barn and property to avoid attracting opossums into feed sources is important,” Dr. Johnson says. “Unfortunately, despite our best efforts it can be nearly impossible to keep all opossums off our farm. Another precaution I recommend is to try and minimize your horse’s stress as much as possible. Since there is no effective EPM vaccine available, keeping the horse’s immune system healthy by minimizing his stress is important.”

Take-home message

From diagnosis to treatment and prevention, your veterinarian is your best EPM resource. If you are concerned about EPM and/or think your horse might be showing neurological signs, call your veterinarian immediately. To learn more about EPM and access complete product information on PROTAZIL, visit


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