EPM Horse Disease

EPM, or equine protozoal myeloencephalitis, is caused by two possibly different parasites. Its effect on horses varies drastically. Some horses never show signs of EPM while others show small signs such as minor lameness. But if left untreated, EPM can cause irreversible brain damage in some horses. It is a problem across North America, and is commonly seen in performance horses that are under stress.

  1. Origin and Causes

    • EPM is caused by Sarcocystis neurona or Neospora flughesi parasites. Horses are exposed to these parasites from opossum feces while foraging for food or water. After exposure, horses form antibodies around the parasites. Fifty percent of the time the parasites do not make it any farther. But there's an equal chance that they will reach a horse's central nervous system and duplicate. Among the things that cause an onset of EPM are the amount of parasite eggs a horse ingests, low immunity and--very important--stress. Major stress factors include long hauling, excessive work, new owners, the loss of a companion and a change in the weather.

    Effects

    • Once the parasites hit a horse's central nervous system, the effects of EPM become noticeable, though all horses will show somewhat different signs. In some horses, facial muscles droop on one side, making the face look very asymmetrical. Or a horse will become slightly lame or stumble during exercise. In other cases a horse's hind quarters will wobble or it will swing its feet outward, lock its stifles or rest its feet oddly.

    Testing

    • There are three ways to test for EPM. A blood test can detect the S.neutrona antibodies, but this test can yield false results. For a horse to have full-blown EPM the parasite needs to be in the spinal cord, so the other two tests involve spinal taps. One test is a search for antibodies; it also can create false positive but not as frequently as the blood test. The most reliable test is the polymerase chain reaction (PCR) test, which uses gene amplification technology to detect S.neutrona.

    Treatment

    • Antibiotics given for about 12 weeks is the best treatment. A combination of Vitamin E, folic acid and thiamin has also been shown to help. Treatment must be consistent and should be followed by tests to make sure the parasite it gone; 28 percent of EPM cases relapse, usually because of inconsistent treatment or because the treatment period is too short.

    Considerations

    • Other diseases cause symptoms similar to those of EPM. Among them are eastern equine encephalitis, equine herpes virus and early orthopedic disease. So your vet is almost certain to check for--and rule out--other things before doing a spinal tap. In addition, EPM develops slowly, allowing time for identifying the problem, if any.