EPM: Still an Enigma or Under Control?

Dynamic discussions about future equine protozoal myeloencephalitis (EPM) diagnostic methods and current EPM treatments were sparked at a June 11 meeting of the Equine Protozoal Myeloencephalitis Society (EPMS) in Minneapolis, Minn. The event, titled "EPM: Still an Enigma or Under Control?" was held in conjunction with the American College of Veterinary Internal Medicine annual convention, and it attracted more than 50 veterinarians.

EPM is caused by the single-celled protozoan parasite S. neurona, which induces brain and spinal cord inflammation. (Learn more at www.TheHorse.com/epm.)

Five speakers reviewed their respective EPM study areas. David Granstrom, DVM, PhD, past president of EPMS and associate director of the Animal and Natural Resources Institute of the USDA, Agriculture Research Service, was a moderator at the meeting and reviewed some of the covered research. (He developed the first diagnostic test for EPM--the Western blot test--and authored the first and second editions of Understanding EPM.)

William Saville, DVM, PhD, Dipl. ACVIM, extension epidemiologist at The Ohio State University, discussed the current state of EPM from a broad perspective. Frank Andrews, DVM, Dipl. ACVIM, PhD, a University of Tennessee professor, spoke on the latest in clinical EPM diagnosis. Dan Howe, PhD, associate professor at the University of Kentucky Gluck Equine Research Center, reviewed potential diagnostic tests for S. neurona.

Howe has used recombinant DNA technology to identify and produce four surface antigens (proteins) of S. neurona; several have been evaluated for use in Western blot tests to detect S. neurona-specific antibodies in the serum and cerebrospinal fluid of affected horses. Four antigens have been adapted for use in recombinant ELISA tests--two seem to be working to detect anti-S. neurona antibodies.

Understanding the immune response to these surface antigens should help scientists better decipher what happens as EPM takes its hold. Recombinant ELISA tests are quantitative and highly specific, so they can provide a reading of how much antibody is present and the types of antibody being produced. Antibody types are known to be associated with specific aspects of the immune response, so the test could uncover important clues about exposure or infection status, which is not possible on the Western blot (that only detects the presence of S. neurona, meaning either exposure or infection).

"This could be a highly effective diagnostic tool and may help us understand why only one in 1000 exposed horses becomes clinically ill," said Granstrom.

Martin Furr, DVM, PhD, Dipl. ACVIM, associate professor at Virginia Tech, and Saville reviewed the progress of the EPM disease model. Saville's transport stress model, which reliably causes EPM clinical signs, "makes it possible to test vaccines for efficacy, to test drugs, and to possibly try and understand how EPM works," said Granstrom.

Rob MacKay, BVSc, PhD, Dipl. ACVIM, professor at the University of Florida, reviewed EPM treatment protocols and gave results from an unofficial survey of 18 prominent clinicians (at large referral clinics and university hospitals) to find out what EPM treatment these vets tend to reach for first. He found that vets treated with Ponazuril (Marquis) predominantly, and if the desired response wasn't achieved, they repeated or increased the dosage or moved on to sulfadiazine/pyrimethamine or nitazoxanide (Navigator). Some used a combination of Ponazuril and sulfadiazine/pyrimethamine. A discussion ensued among attending vets about their EPM treatment experiences.

This sharing of information signifies the cooperation needed to better advance EPM research.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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