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EPM- Part II: Symptoms, Diagnosis and Treatment

How do I know if my horse has EPM?

Equine protozoal myeloencephalitis, known as EPM, attacks the horse’s central nervous system and causes inflammation and damage to the brain and/or spinal cord.  EPM is passed on to the horse when they consume feed contaminated by opossum feces. (See: EPM – Part I: What is EPM and how did my horse get it?) EPM is defined as a progressive, degenerative disease, which means as time passes, the inflammation can become widespread and the damage can increase in severity. Once affected, the function of the tissues in the central nervous system may continue to deteriorate. EPM can be a fatal. Unfortunately, the symptoms of EPM can be difficult to distinguish from other diseases, such as wobbler syndrome, Herpesvirus 1, West Nile virus, rabies, or even equine encephalitis, so this makes it hard to diagnose.

Symptoms of EPM

If your horse has been unlucky enough to ingest the sporulated oocysts that carry the immature EPM protozoa which will infect your horse, the protozoa will hitch a ride on the horse’s white blood cells and migrate through the blood-brain barrier where they will target tissues in either the brain or the spinal cord, or both. Once in the tissue, these protozoa cause inflammation that damages the cells, causing a loss of function.

A key feature in EPM is that the symptoms are asymmetric – which means that they can be worse on one side of the body. Signs of illness may come on suddenly or progress slowly. Some signs are almost imperceptible at first but progressively get worse. It is more common to see symptoms related to spinal cord involvement than brain damage. Symptoms can range from very mild to very severe.

Indication of spinal cord involvement:

  • Asymmetric or symmetric weakness, and poor coordination or unsteadiness of one, or all limbs.
  • Areas of spontaneous sweating
  • Loss of reflexes
  • Loss of sensation in the skin
  • Obvious muscle atrophy

If the spinal cord is affected farther back by the tail, signs of cauda equina syndrome can develop, such as:

  • Neurological symptoms in the lower body
  • Altered sensation in the saddle area
  • Incontinence (bladder and/or bowel)
  • Lower back pain or sharp pains in the legs

 Indications of brain involvement:

  • Depression
  • Head tilting
  • Facial paralysis

If the cranial nerve nucleus is involved, seizures, visual deficits and behavioral changes are often noted.

Things to be on the lookout for at the walk or during a neurological exam:

  • Asymmetric stride length
  • Beating movements of the eyes
  • Circumduction of the hindleg (swinging it very wide)
  • Floating or marching of the front limbs
  • Head tilting or facial paralysis
  • Pelvic sway
  • Toe dragging

Things to be on the lookout for when riding:

  • Difficulty staying on a specific lead or trouble changing leads
  • Difficulty maintaining balance in a turn
  • Excessively high head carriage
  • Frequent bucking
  • Head tossing

Are some horses more likely to contract EPM than others?

  • Horses ages 1 to 5 years old are at highest risk of contracting EPM.
  • Horses on farms where previous cases of EPM have been diagnosed are more likely to develop the disease.
  • EPM is seen more often in the spring, summer and fall.
  • Horses that are stressed or those with compromised immune systems are more likely to contract the disease.

Testing for EPM:

If you suspect your horse has EPM your veterinarian will conduct a full neurological exam and perform certain tests. Testing both the cerebrospinal fluid (CSF) along with a blood serum sample is best. However, spinal taps can be risky and expensive so in many cases a positive serum IgG test combined with neurological signs and a history consistent with exposure to EPM will serve as a positive diagnosis.

My horse has EPM; now what do I do?

There are several treatment options for your horse. Your veterinarian will work with you to pick the best one for your horse’s situation. The earlier you can start treatment, the better. Severely damaged nerve tissues may not recover.

Marquis® (ponazuril)

Available in a paste form and administered for 28 days. Dosage depends on the horse’s body weight.

  • Sometimes it will be combined with dimethyl sulfoxide (DMSO) to increase bioavailability
  • Although not 100% effective, it has a stated success rate of 70% improvement or resolution

Protazil® (diclazuril)

  • Available in an alfalfa-based pellet and administered for 28 days. Dosage depends on the horse’s body weight.
  • Studies show it is as effective as ponazuril.

ReBalance®  (sulfadiazine and pyrimethamine)

  • Available in an oral suspension. Administered once daily for a minimum of 3 to 6 months. Dosage depends on the horse’s body weight.
  • Effectiveness is thought to be limited, providing only temporary relief. When withdrawn the disease often recurs.
  • Requires supplemental folate, especially in pregnant mares.

Recommended supportive therapies:

Along with the drug of choice, your veterinarian will also recommend other supplements and drugs that will keep your horse comfortable and help him or her recover faster.

Elevate® W.S.* (natural vitamin E)

  • Passes through the blood-brain barrier to impact CSF
  • Dosage is 10,000 IU per day
  • Can be fed at high levels for long periods of time with no adverse effects
  • Builds immune response
  • Supports healing of damaged neurological tissues

* Elevate W.S is the only vitamin E research-proven to cross the blood-brain barrier.

NSAIDs

  • To control pain and inflammation as needed.
  • Dosages and length of treatment vary with each individual.

Imunostimulators

  • To support a robust immune response that helps medications do their job.
  • Dosages and length of treatment vary with each individual.

Will my horse recover?

How well your horse recovers depends a lot on how sick he is to start with, and how quickly he was treated. Horses that have mild symptoms and are treated early have the best prognosis. In fact, 80% to 90% recover completely. Horses that have mild cases tend to have a lower rate of relapse. If your horse has a severe case of EPM, the prognosis is not as good. 10% or less achieve full recovery, and the sicker the horse, the more likely it is they will have a relapse.

An ounce of prevention is worth a pound of cure.

At this time there is no vaccine or known preventative available for EPM; however, you can take some precautions to limit your horse’s exposure to infected opossum feces.

  • Don’t inadvertently attract opossums on to your farm.
    • Clean up any grain that is spilled around outside ground feeders.
    • Don’t leave cat or dog food out where an opossum has access to it.
    • Clean up around your bird feeders and don’t leave birdseed where it is accessible.
    • Secure your trash in a critter-proof container.
  • Prevent opossums from gaining access to the areas where you store your hay and concentrates.
  • Restrict your horses from using natural water sources such as ponds or creeks. These are a favorite habitat for opossums and a source of contaminated water.

If you suspect your horse has EPM contact your veterinarian as soon as possible. Together you and your Vet can decide on the best course of treatment for your horse.

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