Atypical Myopathy: Why Are Only Some Horses Affected?

Equine atypical myopathy is an unusual, deadly disease which is poorly-understood. If a group of horses is turned out together, only some will be affected by the debilitating disease, caused by the ingestion of the seeds or saplings of specific trees in the Acer family.

Equine atypical myopathy typically affects horses that live on pasture in the spring and fall. It has been seen in Europe since the mid-1990s. Some 2,500 cases have been reported in the last decade.

Researchers believe intestinal bacteria may play a role in why some horses get the disease while herdmates don’t. Drs. Christina Wimmer-Scherr, Bernard Taminiau, Benoît Renaud, Gunther van Loon, Katrien Palmers, Dominique Votion, Hélène Amory, Georges Daube and Carla Cesarini hypothesized that fecal microbiota may play a role in whether or not horses became affected by the disease.

The study team used fecal samples from 59 horses with atypical myopathy that were referred to Belgian clinics: 29 horses that survived and 30 that didn’t. The team also used 26 healthy horses that shared pastures with the affected horses during the outbreak periods.

The team concluded that horses suffering from atypical myopathy have different fecal microbiota than their healthy counterparts. The changes were more severe in horses that didn’t survive the disease.

Horses impacted by atypical myopathy will suddenly become stiff and weak; they will have a rapid heart rate and dark urine. As the disease progresses, the horse may be unable to rise, experience breathing issues and eventually die. There is no cure and treatment of symptoms is often unsuccessful. The mortality rate is between 43 and 97 percent.

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