Study: Polyparasitism An Unlikely EPM Player in the Eastern U.S.

Scientists don’t know why some horses develop EPM and others don’t, but it’s probably not due to infection with multiple protozoal parasites, researchers found.
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Study: Polyparasitism An Unlikely EPM Player in the Eastern U.S.
Scientists don’t know why some horses develop the debilitating neurologic disease EPM and others don’t. | Photo: iStock
Scientists don’t know why some horses develop the debilitating neurologic disease equine protozoal myeloencephalitis (EPM) and others don’t. But clues might lie in how the causative protozoan parasite Sarcocystis neurona affects other species—namely sea mammals, which suffer more severe disease when both S. neurona and Toxoplasma gondii, another protozoal parasite, are on board.

Sarah Schale, DVM, a clinical fellow in Large Animal Internal Medicine at Oregon State University’s College of Veterinary Medicine, in Corvallis, recently assessed whether horses with S. neurona-caused EPM had also been exposed to the protozoa Neospora hughesi and T. gondii. She presented her results at the Second EPM Society Workshop, held Oct. 25-27, 2017, in Tahoe City, California.

Schale explained that T. gondii’s definitive host is the cat (a reason doctors recommend pregnant women avoid cleaning litterboxes because of the risk for fetal toxoplasmosis infection). “Seroprevalence in horses is reportedly low in the United States, and horses are generally considered to be resistant to toxoplasmosis,” she said. “N. hughesi is the second causative agent of EPM, whose life cycle is largely unknown. Seroprevalence is also relatively low in horses in the U.S. and it has been rarely known to cause clinical disease.”

Her study included 101 neurologic cases seen at the University of Pennsylvania’s New Bolton Center, in Kennett Square; 49 horses had EPM (48 due to S. neurona, one caused by N. hughesi) and 52—the control group—had cervical vertebral stenotic myopathy (CVSM), a structural condition causing spinal cord compression.

“We found that a significantly increased proportion of the EPM cases were likely to be positive for S. neurona on serum, CSF (cerebrospinal fluid), and serum-CSF titer ratios compared to the CVSM cases,” she said, which isn’t unexpected. For N. hughesi, “about 14% of our cases total were positive for Neospora on serum, however, there was no statistically significant difference (in the N. hughesi serum titers, which are concentrations of antibodies) between EPM and CVSM cases

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Written by:

Stephanie L. Church, Editorial Director, grew up riding and caring for her family’s horses in Central Virginia and received a B.A. in journalism and equestrian studies from Averett University. She joined The Horse in 1999 and has led the editorial team since 2010. A 4-H and Pony Club graduate, she enjoys dressage, eventing, and trail riding with her former graded-stakes-winning Thoroughbred gelding, It Happened Again (“Happy”). Stephanie and Happy are based in Lexington, Kentucky.

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