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Equine Protozoal Myeloencephalitis (EPM) is a master of disguise. This serious disease can be difficult to diagnose because its signs often mimic other health problems in the horse and signs can range from mild to severe.
More than 50 percent of all horses in the United States may have been exposed to the organism that causes EPM. The causative organism is a protozoal parasite called Sarcocysticneurona. The disease is not transmitted from horse to horse. Rather, the protozoa are spread by the definitive host, the opossum, which acquires the organism from cats, raccoons, skunks and armadillos, and possibly even from harbor seals and sea otters. The infective stage of the organism (the sporocysts) is passed in the opossum’s feces. The horse comes into contact with the infective sporocysts while grazing or eating contaminated feed or drinking water.
Once ingested, the sporocysts migrate from the intestinal tract into the bloodstream and cross the blood/brain barrier. There they begin to attack the horse’s central nervous system. The onset of the disease may be slow or sudden. If left undiagnosed and untreated, EPM can cause devastating and lasting neurological damage.
The clinical signs of EPM can be quite varied. Clinical signs are usually 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:
Several factors may influence the progression of the disease; however, these four things appear to be important:
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. But, 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 exposed to the protozoan Sarcosysticneurona 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.
Your veterinarian will first conduct a thorough physical and neurological 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 of part of the horse more than another.
If your equine practitioner suspects EPM, he or she may order blood and cerebrospinal fluid (CSF) analysis. Cerebrospinal fluid may be collected by way of a special needle inserted into the spinal cord canal either in a site on the lower back or at the poll. Potential risks are involved with the procedure that should be discussed with your veterinarian.A positive blood test only means that 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.
The sooner treatment begins; the better the horse’s chances are for recovery. Sixty to seventy percent of EPM cases aggressively treated show significant or complete reversal of symptoms. Many horses are able to return to normal activity. Here are some things you should know about treating EPM:
Based on published research, there are several things horse owners can do to protect their horses from infection with EPM. There is currently a vaccine to immunize against Sarcocystisneurona; however, the efficacy is unknown at this time. At best, good horse-keeping practices will discourage unwanted visitors such as opossums and other rodents from contamination hay, grain and bedding.
Here are a few suggestions:
EPM was initially identified 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, University of Missouri, Virginia Tech, University of Maryland and Michigan State University, as well as other institutions, is leading to advancements in EPM diagnosis, treatment and a better understanding of the lifecycle ofSarcocystisneurona.
**This information provided courtesy of the AAEP and Bayer Animal Health. For more information please reference www.yourhorseshealth.com