Equine Atypical Myopathy (EAM)

Atypical myopathy (EAM), is also called atypical myoglobinuria of horses at grass is a frequently fatal disease, where different muscle groups are severely affected and degenerate rapidly. The groups of mucles include postural, respiratory and cardiac muscles.
EAM affects equines of all breeds (draught horses, sport horses, ponies, donkeys and Zebras) who are out grazing most of the time.
EAM is not a contagious disease. However, as its appearance is linked to environmental conditions, horses grazing in a same field can be affected simultaneously.  This disease appears mainly in Spring and Autumn.

It is now commonly accepted that the cause is an environmental toxin which affects the muscular metabolism.

In Europe this amino acid is also found in the seeds and seedlings of Acer pseudoplatanus or sycamore trees, which are most frequently linked to atypical myopathy cases in France and Belgium. However Acer Negundo (Boxelder) is an invasive species, which is expanding rapidly, especially in the south-west of France, and could therefore also be the cause of atypical myopathy in Europe.

The Acer pseudoplatanus, can reach a height of 20 to 30m. Its leaves are dark green with 5 rounded, palmate lobes.It is found in mixed forests of western Europe, through to the Baltic sea. The helicopter-shaped seeds (samara) promote wind dissemination, which increases the area affected by a tree or grove of trees.  

Once hypoglycin A has been ingested, it is metabolised and becomes a highly toxic compound “MCPA-CoA”, which causes severe biochemeical disorders.

It appears difficult to eliminate samara from fields. Even if there are no Acer trees planted near the fields, the helicopter shaped seeds can travel up to 100m from the tree on the wind.

Advice resulting from epidimiological studies :
•    Supplement horses living out at pasture;
•    Reduce the time spent in the pastures during the high risk seasons; stable horses when there is a lot of rain or strong winds; give access to a salt lick
•    Use water from the water network, clean out the drinking troughs on a regular basis.

As the toxin may also be present in the seeds of other trees, research in Europe is concerned with:
•    Implementing tools (dosage of hypoglycin) to identify the other potential sources of poisoning: other trees, hays, drinking water …...
•    Developing a test, from a blood sample, to enable confirmation of diagnosis and establish a survival prognosis

Recognize your Acer trees from observing their leaves and flowers

All Acer trees are not incriminated! In order to assess the risk, you need to recognize those that surround your pastures.

There is currently no known antidote for the toxin. A symptomatic treatment is therefore implemented: administering vitamins and anti-oxidants to support muscle function, and the energetic imbalance of the metabolism. Energy intake should be given with sugars, since the horse’s muscles cannot temporarily use lipids.

Since 2005, there is an alert network for atypical myopathy: AMAG (Atypical Myopathy Alert Group). Set up and managed by the Liège University (Belgium), this group includes research scientists, and European veterinarians confronted with EAM.

Since 2002, when the first cases were diagnosed in France, the RESPE (www.respe.net) (Epidemio-surveillance network in Equine pathology) also takes an active part in the European network

AMAG collects epidemiological and clinical information from horse owners and veterinarians (practitioners, in private clinics and universities) and keeps the professionals in the horse sector updated on any clinical outbreaks. Information can be found on the website : http://labos.ulg.ac.be/myopathie-atypique/

If you are aware of a case, PLEASE declare it:

• As an owner via the following link: http://labos.ulg.ac.be/myopathie-atypique/questionnaire-proprietaire/
• As a veterinarian, via the following link: http://labos.ulg.ac.be/myopathie-atypique/diagnostic_veterinaire/