Recognize EPM—Master of Disguise

When a horse is stricken with Equine Protozoal Myeloencephalitis (EPM) the veterinarian may have to come to the barn on an emergency basis to do a list of tests. EPM has numerous signs and symptoms that initially creep up slowly and can easily be missed. The condition is known as a "master of disguise". The afflicted horse becomes increasingly unsteady and weak in the hind and will often appear underdeveloped in comparison to the heavily developed front end. When muscle mass decreases it’s known as muscle atrophy. It often isn't until the horse suddenly seems wobbly on its legs, assumes a splay-footed stance, leans against stall wall for support, caves in, or collapses in the rear that the owner realizes something is very wrong. After the diagnose is made the primary concerns usually are how to treat the horse during the acute phase and then, how to rehabilitate it.

Recognizing an Acute Phase of EPM

faces of EPM

The faces of EPM

 Neurological deficits that typically show in the face may include: 

  • loss of sensation along the face and neck
  • paralysis of muscles of the face or mouth
  • difficulty swallowing
  • drooping eye lid and lip
  • floppy ear, one pointing sideways
  • head tilt with poor balance

If you notice weakness combined with a lack of coordination, lameness, difficulty traveling on slopes, muscle atrophy, inability to get up, paralysis, or seizures do not wait, but immediately call your veterinarian to have the horse evaluated. The sooner you catch it, the better the outcome can be. Affected horses typically rise front end first and "dog-sit" on the haunches with the front limbs up. In this video the horse struggles to rise. You can clearly see it has great difficulty getting up with the hind end giving out underneath its weight. In such a situation it is very important to keep the horse calm to prevent injury from falling, prevent casting against the wall and thrashing from panic.

Using the EPM Progression Scale to Grade Improvement

Will the horse make it? Fortunately there is hope! The American Society of Equine Practitioners notes that symptoms of EPM can be significantly improved or even completely reversed in 60 to 70 percent of horses if affected animals receive aggressive veterinary treatment early. Improvement is defined as a decrease of at least one grade.The following standardized neurological scale can be used to grade the horse:

0 – Normal, no deficit detected
1 – Deficit just detected at normal gait
2 – Deficit easily detected and is exaggerated by backing, turning, swaying, loin pressure or neck extension
3 – Deficit very prominent on walking, turning, loin pressure or neck extension
4 – Stumbling, tripping and falling down spontaneously
5 – Recumbent, unable to rise

As far as transmission, your horse can not catch EPM from another horse, however, if your horse and the ill horse live in the same place, your horse may be at risk.

Phases of Treatment and Rehabilitation

A combination of medical and chiropractic work, training and strengthening improves the weak hind end of most horses. This horse has been put on Marquis antiprotozoal oral paste with a higher initial dose and Banamine. Each tube of Marquis will treat a 1200 lb. horse for 7 days. The usual course of treatment is 28 days but unfortunately, treatment might take longer than that and this makes it a costly disease, not just money wise. Medical treatment is followed by weeks of rehabilitation with focus on immune system support, muscle reconditioning and maintenance training, stress avoidance, as well as any dietary considerations. Good nutrition is essential for a healthy immune system.

Chances of Relapse

While the percentage of horses that recover is is relatively high, the bad news is that a percentage—estimates range from 10-25%, relapse days, weeks or even months after treatment. Exactly why horses relapse is unclear, but there are three possible reasons:

  1. the parasite was hiding in a form of hibernation within the horse’s body
  2. a small amount of the infection was never completely killed off
  3. the horse was re-exposed to the parasite

The best way to prevent an EPM relapse is providing strong immune system support and reducing stress, keeping opossums (the host) and other intermediate hosts (cats, raccoons, skunks and armadillos) off your property and out of the feed room and minimizing contamination of feed by keeping a tight lid on the feed barrels. Many vets are recommending continuing EPM treatment periodically on a long term basis—at least with Marquis; there also is a stronger drug called Navigator, but the side effects could be too much for you to handle at the farm—very close, constant monitoring is necessary. And also, a caution note for using steroids, because steroids could have a detrimental effect by suppressing the horse’s immune system. Here is a link to Yahoo's online EPM Support Group.

1 comment for “Recognize EPM—Master of Disguise

  1. Elusive Elegance
    March 28, 2015 at 9:25 PM

    EPM is one of the hardest diseases on both the owner and the horse, not only because the cure can take months, but also because it is expensive, requires lots of time off and requires constant monitoring and record keeping and the outcome is hard to predict. It requires hours of time, lots of record keeping, and an open bank account. It is not to be taken lightly, yet the decision needs to be made quickly. Here are important tips, challenges and considerations when treating your horse for EPM:

Leave a Reply

Your email address will not be published. Required fields are marked *