Search for the Cause of Equine Atypical Myopathy

Equine atypical myopathy (EAM), a seasonal, pasture-associated muscle disorder of unknown etiology (cause), presents a particular challenge to veterinarians. The disease is characterized by a generalized complete degeneration of muscle fibers, which
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Equine atypical myopathy (EAM), a seasonal, pasture-associated muscle disorder of unknown etiology (cause), presents a particular challenge to veterinarians. The disease is characterized by a generalized complete degeneration of muscle fibers, which leads to sudden death due to the collapse of the cardiorespiratory system in more than 90% of cases. The economic impact is often devastating.

Affected horses can either die peracutely (acutely) or show profuse sweating, muscle fasciculation (twitching), weakness, pigmenturia (urine discoloration), reluctance to move, recumbency (inability to stand), difficulty breathing, and death after 12-72 hours. Since the etiology is unknown, no effective prophylaxis (preventive treatment) exists and affected horses can only be treated symptomatically.

Large outbreaks have been reported since the 1980s in parts of Europe including the United Kingdom, France, Belgium, Germany, the Netherlands, Switzerland, Luxembourg, and Denmark. In 2010, 224 cases were communicated to the Atypical Myopathy Alert Group, managed by Dominique Votion, DVM, PhD, at the University of Liège in Blegium.

A very similar, if not the same, disease has also been observed in the United States and termed seasonal pasture myopathy. From 1998 to 2005, 14 cases were described in Minnesota. White snakeroot (a perennial herb) toxicosis was ruled out as a potential cause since its toxin was not found in liver or urine samples of affected horses. Seasonal pasture myopathy is thought to be caused by the same etiological agent as EAM

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