Equine Protozoal Myeloencephalitis (EPM) in Horses

Diagnosing EPM in Horses

Diagnosing EPM can be tricky, as it can come on slowly and resemble other neurological diseases initially, such as viral encephalitis, West Nile disease, meningitis, or even rabies. A definitive diagnosis can only be obtained by examining the brain tissue of an infected horse after its death. However, equine veterinarians diagnose their EPM patients indirectly by observing the characteristic signs and symptoms, ruling out other causes of similar symptoms, such as trauma or other infectious diseases, and performing blood tests or tests on the horse's spinal fluid to look for antibodies to S. neurona, which indicate that the horse has been exposed to the organism.

Treatment

Once the diagnosis has been confirmed, the most effective course of treatment can begin. There are currently three different FDA-approved treatments for EPM.

1. Ponazuril (an anti-protozoal drug) by mouth for 28 days
2. Diclazuril (also an anti-protozoal) by mouth for 28 days
3. A combination of sulfadiazine (an antibiotic) and pyrimethamine (an anti-parasitic drug) by mouth for at least 90 days3

Along with one of the above treatments, many equine vets also prescribe anti-inflammatories such as steroids, vitamin E supplementation, or immune-system-modifying drugs.

Prognosis for Horses With EPM

With treatment, up to 60 percent of horses with EPM will improve, but less than 25 percent recover completely. Relapses are also common for as long as two years after the initial treatment with anti-protozoal medications.3 Still, your horse has a good chance of regaining at least some of its former health with prompt intervention. If left untreated, the prognosis for horses with EPM is very poor, as the condition can deteriorate to seizures and death.

How to Prevent Equine Protozoal Myeloencephalitis

There is no vaccine for EPM. Prevention consists of minimizing the presence of opossums on your property as much as possible. Wire-mesh fencing can help keep these marsupials out of your stable area, although because opossums are good climbers, you may have to resort to electrified fencing if they are especially persistent.

Opossums are generally looking for food and are not picky eaters. They will raid trashcans, eat dog food that's left outside, consume your horse's grains, and even eat carcasses of dead animals that they find on the road or within your property. It's essential that all food stores be secure and any animal carcasses buried promptly. Clean up any spilled feed right away, and make sure trashcans have tightly fitted lids.

If opossums make their home on your property, they should be humanely trapped and removed. Other options are motion-activated lights or sprinklers, which can frighten the animals away.