The identification of the probable cause of equine grass sickness (EGS) is a “game changer” in understanding of the disease – and an important step towards reducing deaths.
Experts believe they have found the neurotoxin responsible for causing EGS, which has been elusive for over 100 years. Research involving The Royal (Dick) School of Veterinary Studies’ Equine Hospital, published in the British Equine Veterinary Association’s (BEVA) Equine Veterinary Journal (EVJ), pinpoints a toxin with similar actions to snake venom toxins, produced by microorganisms in pasture.
The equine hospital’s Professor Bruce McGorum said: “Identifying a probable cause of equine grass sickness represents a significant breakthrough. We hope this discovery will lead to novel treatments and improved diagnostics for this devastating condition. We are very grateful for the generous support from horse owners, veterinary surgeons, scientists, charities and funding bodies.
“Further work is under way to determine the source of this neurotoxin; it is likely to be produced by a microbe such as a bacterium or fungus that grows on grass during cold and dry weather, which typically occurs before cases of the disease are identified.”
Grass sickness is a frequently fatal condition that causes degenerative changes to the central and autonomic (involuntary) nervous systems.
For this study, the researchers considered damage to muscle tissue in affected horses and found “major abnormalities” in their neuromuscular junctions; sites of communication between nerves and muscles crucial for muscle function.
These abnormalities are believed to represent damage caused by a type of neurotoxic enzyme, phospholipase A2. The toxin is in some snakes’ venom; it is possible drugs in development for treating people paralysed by snakebite could help horses with EGS.
The equine hospital’s Prof Scott Pirie said: “This work has clearly demonstrated the value of considering disease pathology, even subtle structural changes only visible at extremely high magnification, in the quest to identify the causes of disease, particularly those attributable to the action of toxins.
“The discovery of this distinct signature of toxin activity is a major game-changer in our understanding of this devastating disease.”
The study was carried out with Newcastle University, Istituto Zooprofilattico Sperimentale delle Venezie, and the University of Padova. It was funded by the Royal College of Veterinary Surgeons’ charitable trust and the Moredun Foundation Equine Grass Sickness Fund.
Incredibly proud
“EVJ is incredibly proud to play a small part in getting this information to vets and horse owners,” said EVJ editor Professor Celia Marr. “As an equine clinician, I know this is a really important step towards addressing high losses associated with EGS.”
BEVA’s veterinary projects officer Lucy Grieve said dealing with grass sickness can be “horribly distressing” for vets.
“And it is hugely traumatic for the owner to know the likely outcome of this devastating disease,” she told H&H.
“Whilst we are some way off having means of prevention and treatment to save horses from this condition, this exciting work is an enormous leap in the right direction.
“To think that one day grass sickness could be a thing of the past is very exciting. As, of course, is the wider benefits of the work, the potential impact of which may be far-reaching across veterinary and human medicine.”
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