Fatal equine disease may be caused by a neurotoxic enzyme with similarities to toxins in snake venoms, offering potential for novel diagnostic tests and treatments. Experts believe they have identified the neurotoxin that is responsible for a deadly disease in grazing horses, whose cause has eluded vets for more than a century.A neurotoxin which has similar actions to snake venom toxins, but is produced by microorganisms in pasture, is thought to be the cause of equine grass sickness - according to research involving the Royal (Dick) School of Veterinary Studies’ Equine Hospital.The finding offers promise of new treatments for equine grass sickness, which causes intestinal paralysis, colic, inability to swallow and muscle tremors, leads to death in 1 per cent of horses grazing in high-risk premises, and currently has no cure. Toxin impact Researchers examined evidence of damage in muscle tissue from horses affected by equine grass sickness.Electron microscopic imaging revealed that affected horses have major abnormalities in the structure of their neuromuscular junctions – sites of communication between nerves and muscles that are crucial for normal muscle function.These abnormalities are believed to represent damage caused by a type of neurotoxic enzyme, termed phospholipase A2.This toxin is believed to cause degeneration of the neuromuscular junction, leading to paralysis of the entire gastrointestinal tract. This results in inability to swallow, gastrointestinal distension, colic and constipation, coupled with muscle weakness and tremors.Work is under way to identify the source of this toxin, which is expected to be a microbe such as a bacterium or fungus growing on pasture during cold and dry weather, which commonly precedes incidences of the disease. A pony with equine grass sickness shows muscle wasting and weakness, weight loss and droopy eyelids. Therapeutic insights The toxin associated with equine grass sickness is also present in the venom of many poisonous snakes, and consequently there are many similarities between the signs of grass sickness and those of snakebites. While there is no suggestion that venomous snakes cause grass sickness, it is possible that some of the drugs under development to treat and promote nerve regeneration in people paralysed by snake venoms can also aid recovery of horses from grass sickness. The neurotoxin newly linked to equine grass sickness is expected also to be the cause of apparently identical diseases, known as animal dysautonomias, that affect cats, dogs, hares, rabbits, llamas, alpacas and sheep. This finding contradicts a previous theory that grass sickness may be a form of botulism. The study, published in Equine Veterinary Journal on open access, was carried out in collaboration with Newcastle University, Istituto Zooprofilattico Sperimentale delle Venezie, and the University of Padova. It was funded by the Royal College of Veterinary Surgeon’s Charitable Trust and The Moredun Foundation Equine Grass Sickness Fund. 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. 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 which grows on grass during the cold and dry weather which typically occurs before cases of the disease are identified. Professor Bruce McGorum Royal (Dick) School of Veterinary Studies Equine Hospital 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 in equine grass sickness is a major game-changer in our understanding of this devastating disease. Professor Scott Pirie Royal (Dick) School of Veterinary Studies Equine Hospital Scientific publication About the Royal (Dick) School of Veterinary Studies The Royal (Dick) School of Veterinary Studies is a one-of-a-kind centre of excellence in clinical activity, teaching and research. Our purpose-built campus, set against the backdrop of the beautiful Pentland Hills Regional Park, is home to more than 800 staff and almost 1400 students, all of whom contribute to our exceptional community ethos. The School comprises: The Roslin Institute The Global Academy of Agriculture and Food Systems The Roslin Innovation Centre The Hospital for Small Animals Equine Veterinary Services Farm Animal Services Easter Bush Pathology The Jeanne Marchig International Centre for Animal Welfare Education We represent the largest concentration of animal science-related expertise in Europe, impacting local, regional, national and international communities in terms of economic growth, the provision of clinical services and the advancement of scientific knowledge. This article was published on 2024-12-05
