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Posted: 6th December 2024

Probable cause of EGS identified
Equines suffering from mild EGS can sometimes be treated with nursing and supportive care.
Discovery of neurotoxin could lead to new treatments.

Researchers from across several organisations have collaborated to identify a neurotoxin as the probable cause of equine grass sickness (EGS).

It is hoped that the discovery of this neurotoxin could lead to better diagnostics and novel treatments which would improve outcomes for the disease.

EGS is recognised by a rapid degeneration of a horse’s nerves, which leads to the paralysis of the gastrointestinal tract, an inability to swallow, abdominal pain and more.

There is no effective treatment for the most severe cases of the disease, and so many horses are euthanised on humane grounds. Some mild forms can be treated with nursing and supportive care.

The researchers believe that a neurotoxic enzyme, called phospholipase A2, may be responsible for EGS. The neurotoxin has similar actions to snake venom toxins, however it is produced by pasture microbes.

Electron microscopy was used to identify major abnormalities in affected horses, which researchers say represent a toxin-specific signature for the neurotoxin. These abnormalities were identified in horses’ neuromuscular junctions – microscopic communication sites between nerves and muscles which are crucial for normal muscle function.

Neurotoxic phospholipase A2 toxins are also present in the venom of poisonous snakes and, consequently, similarities have been drawn between signs of EGS and snake envenomation. Although there is currently no suggestion that snakes are causing EGS, it is hoped that the same drugs used to treat nerve regeneration in people paralysed by snake bites could be used to treat EGS.

The neurotoxin has now also been linked to animal dysautonomias, which contradicts previous theories which suggested EGS was a form of botulism.

Now that the toxin has been identified, there is work underway to confirm its source.

Currently, it is considered to be the result of a bacterium or fungus that grows in horses’ pastures. It normally grows in cold and dry weather, which usually precedes an outbreak of the disease.

The discovery was the result of work from several organisations: the Dick Vet Equine Hospital at the University of Edinburgh, Newcastle University, Istituto Zooprofilattico Sperimentale delle Venezie and the University of Padova.

Bruce McGorum, of the Royal (Dick) School of Veterinary Studies, said: “Identifying a probable cause of Equine Grass Sickness represents a significant breakthrough. We hope that this discovery will lead to novel treatments and improved diagnostics for this devastating condition.

“We are very grateful for the generous support we have received from horse owners, veterinary surgeons, scientists, charities and funding bodies.”

The full study can be read here.

Image © Equine Veterinary Journal



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