The clinical signs of EPM can be quite varied. Clinical signs are almost always asymmetrical (not the same on both sides of the horse). Actual signs may depend on the severity and location of the lesions that develop in the brain, brain stem or spinal cord. Signs may include:

 

Horses At Risk

EPM is considered the number one cause of neurologic problems in horses today. Almost every part of the country has reported cases of EPM. However, the incidence of disease is much lower in the western United States especially in regions with small opossum populations. However, due to the transport of horses and feedstuffs from one part of the country to another, almost all horses are at risk.

 

Not all horses who are exposed to the protozoan Sarcocystis neurona will develop the disease and show clinical signs of EPM. Some horses seem to mount an effective immune response and are able to combat the disease before it gains a foothold. Other horses, especially those under stress, can succumb rapidly to the debilitating effects of EPM. Still others may harbor the organisms for months or years and then slowly or suddenly develop symptoms.

 

 Diagnosis

Your veterinarian will first conduct a thorough physical examination to assess your horse's general health and identify any suspicious signs. One notable clue is the disease often tends to affect one side or part of the horse more than another.

If your equine practitioner suspects EPM, he or she will order blood and cerebrospinal fluid (CSF) analysis. A spinal tap, in which a long needle is inserted through the back and into the spinal canal, will be necessary. The blood test alone, while useful, is inconclusive as it may indicate exposure to the organism but not whether the disease has attacked the central nervous system. A positive blood test only means the horse has been exposed to the parasite, not that it has or will develop clinical disease. Currently three laboratories are analyzing blood and spinal fluid for the prescence of S. neurona antibodies. Prompt, accurate diagnosis is essential and treatment should begin immediately.

 

 

 Treatment

New Treatment For EPM

Equine Protozoal Myeloencephalitis (EPM) is a progressive, degenerative disease of the central nervous system of the horse. The disease is characterized by asymmetrical ataxia with or without muscle atrophy. There are several diseases of the central nervous system that can mimic EPM. It is important for the veterinarian to do a thorough neurological examination with appropriate laboratory diagnostic support such as a cerebrospinal (CSF) analysis. Early, accurate diagnosis and treatment offer the best chance for success.

Until recently there were no approved treatment products for EPM. Veterinarians, out of necessity, had to use products that had not been evaluated for efficacy or safety when used in treating horses with EPM. In July of 2001, the FDA approved Marquis (15% w/w ponazuril) Antiprotozoal Oral Paste, the first medication for the treatment of EPM in the United States. Marquis is manufactured by Bayer in Shawnee Mission, Kansas.

Marquis is a prescription medication. It is a unique paste formulation with a gel-like consistency. The active ingredient of Marquis is ponazuril, an anticoccidial compound with cidal activity against the protozoal parasite that causes EPM. The dosage regimen is 5 mg/kg (2.27 mg/lb) body weight given orally, once per day, for 28 consecutive days. This product is packaged with four syringe barrels of paste per box and a calibrated dosing ring for accuracy and ease of administration. Each syringe contains enough paste to treat one, 1200 pound horse for seven days. The four syringes comprise the entire 28 day treatment program. Marquis should be stored at controlled room temperature, between 59 and 86 F. This product has a 24 month shelf life.

Marquis has demonstrated activity against Sarcocystis neurona (the causative agent of EPM) in both the laboratory and field setting. Efficacy studies were conducted in five states by seven different investigators. These studies demonstrated the effectiveness of Marquis against naturally-occurring cases of EPM. Marquis has also been demonstrated to be safe when used according to label directions. Target animal safety studies* at up to six times (6X) the label dose for two times (2X) the label treatment duration, produced sporadic inappetence, occasional loose stools and, in three of four study mares, moderate uterine edema. The safe use of ponazuril in horses intended for breeding purposes, during pregnancy, or in lactating mares, has not been evaluated.

It is important to note that while Marquis may effectively clear the horse of S. neurona, it will have no effect on irreparable, central nervous system damage caused by the parasite prior to treatment. The prognosis for animals treated for EPM may be dependent upon the severity of the disease and the duration of infection before treatment. Early and accurate diagnosis followed by immediate treatment are critical for best clinical results.

* (N=24)

 

 

Methods Of Prevention

Unfortunately, there is little horse owners can do to adequately protect their horses from infection with EPM. At best, good horse-keeping practices will discourage unwanted visitors such as opossums, other rodents and birds from contaminating hay, grain and bedding.

Here are a few suggestions:

 

Ongoing Research

Clinical symptoms for EPM were originally described in 1964. In recent years, awareness among veterinarians and horse owners has grown considerably. Research at the University of Kentucky, the University of Florida, Ohio State University, the University of California at Davis, and Michigan State University, as well as other institutions, is leading to advancements in EPM diagnosis and treatment.

For more information regarding EPM, contact your veterinarian or the American Association of Equine Practitioners, 4070 Iron Works Pike, Lexington, KY 40511, (859) 233-0147.