Study: MADD Likely Caused by Fungus on Maple Leaves

After investigating the deaths of 14 horses that had grazed on pastures near maple leaves, a Dutch research team suggested the fungus responsible for European tar spot that covers the maple leaves causes the deadly disease "MADD."

Multiple acyl-CoA dehydrogenase deficiency, or MADD, is an acquired, noncontagious myopathy (muscle disease) characterized by severe muscle pain. Death occurs in up to 90% of affected horses within 72 hours of first showing signs of MADD.

MADD outbreaks reported in Europe in 2009 involved 371 horses from 10 different countries. Of these, 265 (71%) died.

After examining the pastures where the group of horses was either definitively or tentatively diagnosed with MADD by urine test, the Dutch research team, including Inge Wijnberg, DVM, PhD, Dipl. ECEIM, an assistant professor in equine internal medicine in the department of equine sciences, faculty of veterinary medicine at Utrecht University, found that all pastures where the horses grazed had maple trees nearby.

"The maple leaves were covered with the fungus Rhytisma acerinum, also called European tar spot," relayed Wijnberg. "It is possible that the horses ingested the fungus-covered leaves, which is facilitated due to their high carbohydrate content, and the fungus induced equine-acquired MADD."

But hold on to those torches and chainsaws: Wijnberg added, "No toxicity studies have been performed to date to prove that the fungus is the underlying cause of MADD."

Other causes of MADD have also been suggested, including a toxin produced by the bacterium Clostridium sordellii.

"More studies are needed to determine the cause of MADD and to design prevention and treatment protocols," said lead researcher Han van der Kolk, DVM, PhD, Dipl. ECEIM, also from Utrecht University.

"In eastern Canada, R. acerinum has been found on Norway maple trees. It is possible that the fungus is adapting to attack maples in North America, perhaps due to the decrease in acid rain," noted Wijnberg.

A seasonal myopathy with similar characteristics as the acute myopathy described in this study has been reported in Minnesota.

The study, "Equine acquired multiple acyl-CoA dehydrogenase deficiency (MADD) in 14 horses associated with ingestion of maple leaves (Acer pseudoplatanus) covered with European tar spot (Rhytisma acerinum)," is scheduled to be published in an upcoming edition of the journal Molecular Genetics and Metabolism.

The abstract is currently available on PubMed.

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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