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Care Guide

About Care Guides[x] These care guides are written to help your clients understand common conditions, tests, and procedures, as well as to provide basic information about pet care. They are based on the most up-to-date, documented information, recommendations, and guidelines available in the United States at the time of writing. Pharmaceutical product licensing, availability, and usage recommendations are based on US product information. Use the Download Handout button to generate a PDF for printing or e-mailing to your clients.

Equine Protozoal Myeloencephalitis

    • Equine protozoal myeloencephalitis (EPM) is a common neurologic disease in horses.
    • Diagnosis is based on signs, cerebrospinal fluid testing, and a horse’s response to medication.
    • With drug therapy, horses can recover from EPM.
    • A vaccine is available for preventing EPM.
    • The likeliest source of infection is opossums, so horse owners should follow the guidelines below for keeping opossums away from their horses.

    What You Need to Know

    Equine protozoal myeloencephalitis (EPM) is a disease that causes spinal cord problems and brain inflammation in horses. It is caused by infection with certain microorganisms, one of which is carried by opossums. In the Americas, EPM is caused by a microorganism called Sarcocystis neurona in a horse’s feed or water. Horses can be affected at any age.

    Signs and Diagnosis

    Signs vary according to the location of the infection in the body. Signs are very rare in horses younger than 12 months. Infection of the spinal cord is common, resulting in weakness, loss of coordination, and wasting of the rump muscles (one side of the rump is often smaller than the other). Other signs include sudden sweating, head tilt, facial paralysis, vision problems, behavioral abnormalities, and seizures. Some signs may not occur until years after infection.

    Diagnosis is based on signs, cerebrospinal fluid testing, and your horse’s response to medication.

    Treatment and Prevention

    With medication, horses can recover from EPM; however, neurologic damage can be permanent. Treatment can take 28 days to 6 months, depending on the drug, which is applied as an oral paste. Without treatment, EPM is often fatal.

    A vaccine is available for preventing EPM, and its effectiveness continues to be evaluated by researchers

    The likeliest source of infection is opossum feces, so horse owners should try to keep opossums away from their horses, especially feeding and watering areas. Horse and pet feed should not be left out. Garbage and open feed bags should be kept in closed galvanized metal containers. Bird feeders and fallen fruit should be removed from areas where horses are kept. Opossums can be trapped and relocated.