Understanding Atypical Myopathy

"Atypical myopthay is a serious concern because it is highly fatal and is considered an emerging disease in Europe. Since 2000 more than 1,000 horses have been either diagnosed or thought to be afflicted with this emerging disease," Votion said.

Photo: Megan Arszman

Imagine that one minute your horse is grazing idly in the pasture, and the next minute he's lying down and unable to rise. In Europe and sporadically throughout the United States, this scene is occurring more and more frequently. The cause? A condition called atypical myopathy--the sudden onset of acute myopathy (muscle pain and damage) that is not related to exercise, but rather pasture.

"Atypical myopthay is a serious concern because it is highly fatal and is considered an emerging disease in Europe. Since 2000 more than 1,000 horses have been either diagnosed or thought to be afflicted with this emerging disease, according to the 'Atypical Myopathy Alert Group,' " said Dominique Votion, DVM, PhD, from the Equine Clinic at Belgium's University of Liege, at the 12th Congress of The World Equine Veterinary Association, held Nov. 2-6 in Hyderabad, India.

"Major advances have recently been made to help us understand what causes atypical myopathy and how to prevent it," Votion explained.

Scientists now know that horses with atypical myopathy have a defect in how fats--not carbohydrates--are metabolized by the microscopic "power horse" organelles inside muscle cells called mitochondria. Due to this defect, energy is not produced properly from fats, causing the horse to show signs of muscle weakness and can become recumbent (unable to rise) very quickly.

Votion also noted that previous research indicates the toxin produced by the bacterium Clostridium sordellii is hypothesized to contribute to atypical myopathy

According to Votion, "There is currently no treatment for atypical myopathy, but we have identified several ways to prevent this condition at both the horse and pasture level."

Some of these preventive measures include:

  • Reduced pasture time during inclement weather and during the "risky season" (i.e., autumn and spring);
  • Avoid pastures with a history of horses dying due to atypical myopathy;
  • Remove dead leaves, sticks, and wood and avoid harrowing pastures;
  • Exercise horses regularly;
  • Provide a salt block and supplemental feed; and
  • Practice regular deworming and vaccination.

A full summary of the presentations titled, "Novel insights into the management of atypical myopathy in grazing horses based on a recent series of European outbreaks and advances in etiological investigation," which Vincent Gerber, DVM, PhD, Dipl. ACVIM, ECEIM, from the Equine Clinic at the University of Berne in Switzerland, co-authored, will be available for free on the International Veterinary Information System.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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