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Washington County Chapter |
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EPM EPM: A Debilitating Disease of Horses 2938 Vet. Med. Basic Sciences Bldg. In the past few years, equine protozoal myeloencephalitis, or EPM, has emerged as a major debilitating disease of horses. Each case of EPM is unique, but common signs include incoordination, lameness, weakness, muscle atrophy, and paralysis. Though the disease rarely kills, about 30% of afflicted horses do not improve even after treatment. The disease is caused by single-celled organism, a protozoan parasite called Sarcocystis neurona, which is spread by the opossum. "The opossum passes the organism in its feces, which are then ingested by horses when they eat contaminated feed, hay, or water," explains Dr. Doug Hutchens, veterinary parasitologist at the University of Illinois College of Veterinary Medicine in Urbana. After ingestion, the tiny parasite invades the spinal cord and central nervous system. When the horse's immune system tries to fight off the invading parasite, inflammation occurs in the spinal cord or brain. Horses can't transmit the disease to other horses. The most common signs of EPM are what veterinarians call ataxia, asymmetric lameness, and atrophy. That is, a horse may be uncoordinated, may be lame on one side or the other, and may lose muscle mass, most commonly over the hips or shoulders. "Horses may have sudden onset of clinical signs or develop the disease slowly over several months," say Dr. Hutchens. "Typically, owners say that afflicted horses stumble or are 'off' in the hind end, most commonly the stifle." The first step to diagnosing EPM must include a thorough physical and neurological examination by an equine veterinarian. If the neurological exam indicates that further testing for EPM is warranted, the next step is to test blood serum and cerebral spinal fluid (CSF) for antibodies to Sarcocytsis neurona. Many more horses are exposed to the organism and manage to fight it off than actually get the disease. Whenever a horse is exposed, whether it gets sick or not, it will make antibodies to the organism and carry these antibodies in its blood. Therefore, a blood test for serum antibodies can confirm exposure to the EPM organism, but it doesn't necessarily mean the horse has the disease. The CSF antibody test presents another diagnostic challenge. Since collecting cerebral spinal fluid for EPM testing involves poking a needle into the lumbosacral space of the spinal cord, problems can arise if the needle grazes a vessel and blood happens to enter the CSF during the procedure. "Any bleeding during the spinal tap can contaminate the CSF with serum antibodies to the EPM organism," says Dr. Hutchens. "What that means is that a disease-free animal may test positive." So don't jump the gun on blood or CSF testing healthy animals for EPM. "The test is useless in a healthy animal without lameness or neurological signs suggestive of EPM," says Dr. Hutchens. "But, if a horse has clinical signs, the tests have high reliability." Therefore, a clinician will usually take into account all the evidence -- a neurological exam and serum and CSF testing -- to diagnose EPM. So what can you do to prevent this parasitic infection? "The presence of opossums where horses are stabled puts horses at risk," says Dr. Hutchens. "Stress is another contributing factor, and show horses and racehorses have a higher risk of contracting EPM due to the increased stress of athletic performance and travel." Dr. Hutchens recommends limiting access of opossums to stables and keeping all feed storage containers covered at all times. "Since most horses are exposed to the organism but only a small percentage actually develop the disease, preventive care to keep a horse healthy and minimize stress appears to be very important," says Dr. Hutchens. So keep up with all routine vaccinations and de-worming programs, groom and exercise horses regularly, and give them a balanced diet. Contact your local equine veterinarian promptly if your horse shows any signs associated with EPM and for more information on how you can help prevent EPM. |