Friday, May. 24, 2024

Veterinary Corner: Protecting Horses From EPM

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The Veterinary Corner series, brought to you by Merck Animal Health, features insights from leading veterinarians on some of the most pressing health issues affecting horses today.

By Bryant Craig, DVM, Merck Animal Health

Image courtesy of Merck Animal Health

EPM. These three little letters can be scary to hear. Fortunately, if your horse is diagnosed with EPM—technically known as equine protozoal myeloencephalitis—the disease can be safely, easily and effectively treated with an FDA-approved product.

EPM is a neurologic disease horses contract from drinking water or eating feed contaminated with opossum scat. Ideally you could protect your horse from EPM by ensuring they aren’t exposed to opossums. Maintaining a clean barn and property makes the environment less attractive to opossums but keeping them away completely is difficult.

That’s why knowing the signs of EPM is important. EPM is a progressive disease and, if left untreated, it can cause lasting damage to your horse’s central nervous system. The sooner you treat it with an FDA-approved product, the better your horse’s chance of recovery.

Contact your veterinarian immediately if your horse exhibits any of these neurological signs:

• Gait abnormalities

• Ataxia (incoordination)

• Stumbling


• Muscle atrophy

• Weakness

• Depression

• Inability to chew or swallow

• Head tilt or ear droop

• Behavior change

• Blindness

• Seizures

While timely treatment is critical, pausing to get a proper diagnosis from your veterinarian is important. Many diseases cause symptoms similar to EPM, but they won’t respond to EPM treatment. A physical and neurologic examination, along with further diagnostics like antibody testing, helps you avoid wasting money and, most importantly, time on unneeded treatments.


After diagnosing EPM, your veterinarian may recommend an FDA-approved product like PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets, the only alfalfa-based top dress EPM treatment. Protazil is well accepted by horses without mess or fuss, so treatment is as easy as scooping the prescribed amount onto your horse’s feed. And it’s effective against EPM: Horses treated with an anticoccidial drug like Protazil are 10 times more likely to improve than untreated horses.1

Unconditional commitment to horse health

To continue advancing understanding of EPM, Merck Animal Health is investing in new research to study the disease and its treatment. This includes a partnership with the University of Kentucky’s Maxwell H. Gluck Equine Research Center to support graduate student research. Through the Merck Equine Research Fellowship, Izabela De Assis Rocha, BVM, PhD candidate, is studying diclazuril (the active ingredient in Protazil) and its effect on Sarcocystis neurona, a causative agent for EPM.

Supporting ongoing research into equine health issues like EPM and developing cutting-edge products like Protazil are just two components of the Merck Animal Health Unconditional commitment to the horse and those who care for them. To learn more about EPM, check out this quick facts sheet.

IMPORTANT SAFETY INFORMATION: PROTAZIL® is contraindicated in horses with known hypersensitivity to diclazuril. The safety of Protazil in horses used for breeding purposes, during pregnancy, or in lactating mares, and use with concomitant therapies in horses has not been evaluated. Do not use in horses intended for human consumption. Not for human use. For complete safety information, refer to the product label.

About The Author

Dr. Craig is associate director of scientific affairs for equine professional services and pharmacovigilance at Merck Animal Health. Prior to joining Merck Animal Health, Dr. Craig owned and operated a private equine veterinary practice for six years in central Oklahoma before joining a top Quarter Horse ranch as resident veterinarian.

1. Reed SM, et al. Equine Protozoal Myeloencephalitis: An Updated Consensus Statement with a Focus on Parasite Biology, Diagnosis, Treatment and Prevention. J Vet Intern Med 2016;30:491–502.

Copyright © 2023 Merck & Co., Inc., Rahway, NJ, USA and its affiliates. All rights reserved.




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