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How Long Can A Horse Live With Equine Protozoal Myeloencephalitis?

Equine Protozoal Myeloencephalitis (EPM) is a serious equine disease that can be very hard to diagnose. Its symptoms are similar to those of a number of other types of horse health problems. Furthermore, signs and symptoms may vary from horse to horse. In some horses symptoms are quite mild, while in others they are quite severe.

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Exposure to EPM is common. In fact throughout the United States, on average about 50% of horses have been exposed to the protozoal parasites (Sarcocystis neurona and Neospora hughesi) which causes this debilitating disease. In some areas of the United States, the exposure rate rises to 90%.

The vast majority of horses are able to fight off these organisms through strong immune defense. Unfortunately a very small percentage succumb to neurological damages wrought by these organisms. Even though EPM is a widespread condition and cases have been reported all over the United States, the fact is only about 1% of horses will succumb to this disease.

How Does EPM Spread?

how does epm spread

This parasite is not spread from one horse to another. Instead it is spread through ingestion of sporocysts that come from the feces of possums. Horses may pick up the sporocysts from grass, contaminated hay, contaminated feed or drinking water.

When a horse ingests sporocysts, the organisms land in the intestinal tract and move into the bloodstream. Once in the bloodstream, the sporocysts are capable of crossing the blood/brain barrier and attacking the central nervous system (CNS).

How Can You Tell Your Horse Has EPM?

For many horses, the immune system launches a rapid response and fights off the organisms. Others succumb. For these, the onset of symptoms may be gradual or sudden.

Here are the symptoms to watch for:

  • Weakness and muscle atrophy are common. Your horse may lose condition in the hindquarters and the top line. They may be lying down more than usual. Occasionally, the muscles of the front legs and the face become atrophied.
  • Your horse’s mouth, face and eyes may become paralyzed. You’ll notice this by a droopy affect around the lips, ears and eyes.
  • Loss of balance may cause your horse to stand splay footed or lean against walls to avoid falling down.
  • Your horse may lose sensation at any place on its body, but most especially on the face and neck.
  • Severely affected horses may have seizures and even collapse.
  • Loss of muscle coordination can cause difficulty in swallowing.
  • Your horse may move in a stiff and stilted way (spasticity).
  • Your horse may suffer from a lack of coordination (ataxia).
  • Hyperhidrosis or excessive sweating is a common sign.
  • Your horse may tilt his head to one side or the other.
  • Your horse may go lame or exhibit ad unusual gait.

Symptoms may vary from horse to horse, and a horse may exhibit just one or a few of these symptoms. The severity and type of symptoms your horse exhibits depend upon the location and severity of lesions the organisms cause on the spinal cord, brainstem and/or brain. Typically the symptoms are asymmetrical in that they occur only on one side and not on both sides.

If you notice symptoms of EPM in your horse, it’s very important that you contact your vet right away. Quick diagnosis and treatment can make a tremendous difference in rate of survival.

Is EPM Always Fatal?

is epm always fatal

If caught early and treated aggressively your horse may survive an attack of EPM. There are four factors that seem to influence the severity of the disease. They are:

  1. The number of organisms your horse has ingested makes a difference. If your horse eats a great deal of contaminated grass, hay or feed, he is likely to have a far more severe case than a horse that has experienced light exposure.
  2. Speed of treatment. The longer your horse goes without treatment, the more opportunity the parasites will have to reproduce and cause damage.
  3. The location of the damage seems to make a difference in the severity of the illness. Damage may occur at any point along the spinal cord, the brainstem or in the brain.
  4. Stress level seems to have a great impact on the severity of the symptoms. If your horse is under a great deal of stress while infected, the symptoms and the damage will be worse.

What Can You Do to Prevent EPM?

Your location strongly influences your horse’s chance of contracting EPM. Because the disease is spread by possums (and possibly by rodents) your horse is far less likely to contract the syndrome in parts of the nation where possum populations are low or nonexistent. Even so, keep in mind that feedstock and hay travels from state to state, and you may very well be feeding your horse a product that has been in contact with possum feces.

To avoid contamination, follow these protocols:

  1. Secure your feed and hay. Keep feed in metal containers with tightly fitting lids, and keep your feed room and hay storage areas locked so that possums and other vermin can’t contaminate your hay.
  2. Feed your horse the right amount in a weighted container or one that is attached to the wall that minimizes spillage. Be sure to clean up any spilled grain right away to avoid attracting mice, rats and possums.
  3. Never feed your horse on the ground. Always feed grain in containers and hay in hay nets or in a manger.
  4. When selecting grains, look for those that have been heat treated as this process kills off the sporocysts.
  5. Keep vermin under control through use of a professional pest service or traps. Don’t use poisons as this may cause you even more problems. Be sure to dispose of vermin carcasses quickly and carefully.
  6. Keep your horse’s water tanks filled with fresh clean water. Clean them frequently to avoid multiplication of harmful organisms.

It is also important to remember that a minority of horses actually succumb to exposure to the parasite. Keeping your horse healthy and well fed, maintaining a regular schedule of veterinary visits and exams and keeping your own property clean and possum/rodent free will go far toward protecting your horse against this dangerous disease.

How Long Can A Horse Live With EPM?

It’s impossible to say how long a horse will live with the disease, and surviving with EPM is not a goal that any responsible horse owner would strive for. It is imperative that the moment you notice any possible symptoms of this neurological disease, you contact your vet, get a diagnosis and begin treatment as appropriate.

Here is a video of a horse who was diagnosed quickly and received aggressive treatment.

This horse recovered.

Here is one of a horse who received diagnosis and treatment but ultimately succumbed to the disease.

Different horses respond differently to treatment, but the faster you can get a diagnosis and begin aggressive treatment, the better your horse’s chance of recovery.

What Will The Vet Do?

Your vet will perform a complete neurological exam. He or she may also want to perform a blood test and take a cerebrospinal fluid sample. Testing procedures and treatment can be costly, but they may save the life of your horse. Based on the results of the exam and the testing, your vet will create a treatment plan.

Treatments involve a combination of drugs and complementary treatment. Both anti-protozoal drugs and anti-inflammatory drugs may be prescribed. Additionally, your vet may recommend that you supplement your horse’s feed with vitamin E as an antioxidant. Vitamin E is known to help support healing of nervous system tissue.

Are There Any Complications Or Side Effects?

Use of EPM drugs can negatively affect your horses iron levels. Throughout treatment, your vet will want to monitor your horses white blood cell count, platelet count and iron levels.

There are some rare complications associated with the use of the antiprotozoal drugs. For example, fertility may be affected in stallions. Pregnant mares may also experience some complications with their pregnancy, and unborn foals may be at risk.

While your horse is being treated, stay in close contact with your vet. Report any changes in behavior and symptoms. Be especially vigilant about side effects such as acute diarrhea.

How Long Does Treatment Take?

Surprisingly, the duration of treatment is rather short considering the seriousness of the condition. Generally speaking, an affected horse may take FDA approved antiprotozoal drugs for about a month. In some cases (and depending upon which drugs are used) treatment can take as long as nine months.

Nicky Ellis
Nicky has been an editor at Horses & Foals since 2017. Horses have been in her life from her earliest memories, and she learned to ride a horse when she was 5. She is a mom of three who spends all her free time with her family and friends, her mare Joy, or just sipping her favorite cup of tea.


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