The researchers, from the Dick Vet Equine Hospital, University of Edinburgh, Newcastle University, Istituto Zooprofilattico Sperimentale delle Venezie, and the University of Padova found that affected horses have major abnormalities in the structure of their neuromuscular junctions, microscopic sites of communication between nerves and muscles that are crucial for normal muscle function.
These abnormalities are believed to represent a toxin specific signature, effectively a ‘smoking gun’, for a neurotoxic enzyme termed a phospholipase A2.
Work is now underway to definitively identify the source of the toxin, in the hope that it will lead to novel treatments and improved diagnostics for this devastating disease.
The researchers think the toxin is likely to be produced by a microbe such as a bacterium or fungus growing on the horse’s pasture during the cold and dry weather which commonly precedes the disease.
Neurotoxic phospholipase A2 toxins are also present in the venom of many poisonous snakes, and there are many similarities between the signs of grass sickness and those of snake envenomation.
While there is no suggestion that venomous snakes cause grass sickness, it is hoped that some of the drugs that are currently being developed to treat and promote nerve regeneration in people paralysed by snake venoms can aid recovery of horses from grass sickness.
The researchers say that the neurotoxin most likely also causes the apparently identical diseases (termed animal dysautonomias) which affect cats, dogs, hares, rabbits, llamas, alpacas and sheep, and that their finding contradicts the previous leading hypothesis that grass sickness is a form of botulism.
This breakthrough is summarised in an editorial in the January 2025 issue of the Equine Veterinary Journal (EVJ).
The editorial, by Bruce McGorum and colleagues, looks at the implications of their article 'Equine grass sickness is associated with major abnormalities in the ultrastructure of skeletal neuromuscular junctions2".
Bruce 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.”
Bruce's editorial is currently available on Early View, free for 12 weeks, and will also be published in the January 2025 print issue of the EVJ.
Reference
Investigation of the relationship between ionised and total calcium in dogs with ionised hypercalcaemia1 was undertaken by Tørnqvist-Johnsen et al. at the Hospital for Small Animals, University of Edinburgh, UK.
Initially, a normal reference interval for ionised calcium, total calcium and albumin, serum and plasma biochemistry was established by analysing samples from 351 healthy adult dogs.
After establishing a reference interval for ionised calcium, the laboratory’s database was searched for adult dogs with ionised hypercalcaemia that had attended the university small animal hospital between 2012 and 2017, a time frame when the same sample handling protocols and instrumentation was in use. The hospital records were searched for patient information and the biochemical parameters statistically analysed.
Of 63 dogs identified with ionised hypercalcaemia, 23 did not have a total hypercalcaemia (37%). 16 of these 23 dogs (70%) had albumin within the reference interval. To summarise the key findings; using total calcium, one third of patients with ionised hypercalcaemia were not identified. There was also no significant relationship between albumin and total calcium in these cases.
Camilla Tørnqvist-Johnsen, lead author of the paper, said: "Hypercalcaemia is a very important clinical abnormality, often revealing severe underlying disease in dogs who do not get idiopathic hypercalcaemia. This study reveals the true importance of doing an ionised calcium measurement when evaluating calcaemic status."
Nick Jeffery, Editor of JSAP said: "This study demonstrates that, if relying on total calcium alone, more than one third of dogs with ionised hypercalcaemia will be classified as normocalcaemic. Furthermore, the study demonstrates that the discordance between ionised and total calcium cannot be routinely explained by a low protein-bound component.
"Whilst reference intervals are key in clinical practice to determine whether a result is an outlier from 95% of a healthy population, it is not inevitable that a patient with an outlying biochemical test result has a clinically relevant disease."
The full article can be found in the April issue of the Journal of Small Animal Practice which is free for BSAVA members. It can also be read online here: https://onlinelibrary.wiley.com/doi/10.1111/jsap.13109
Her Royal Highness, the Princess Royal opened a new ward for canine cancer patients at the University of Edinburgh's Royal (Dick) School of Veterinary Studies Hospital for Small Animals last week.
The Kennel Club Charitable Trust provided £30,000 towards the 26-kennel ward, which is specifically designed to provide recuperative care and comfortable kennelling facilities for dogs at the University's Hospital for Small Animals.
The facilities the new dog ward provides will complement the School's £3 million Riddell-Swan Veterinary Cancer Centre, which opened last year. The cancer care centre houses state-of-the-art equipment including a computerised tomography (CT) scanner and a linear accelerator that can provide radiotherapy treatment.
Caroline Kisko, Secretary of the Kennel Club, said: "The Kennel Club Charitable Trust is extremely pleased that the money it has given to the University of Edinburgh has helped to ensure that its Canine Cancer Care unit could be built.
"The Trust has supported the groundbreaking research being conducted by the University, which is helping to improve our ability to diagnose and treat cancer in dogs, for some time. The Cancer Care Unit will help in a different way, by providing post-treatment and after care for dogs that have been through cancer therapy.
"People love their dogs as a member of their family, so this is a vital part of the care process. It is comforting for them to know that there are comfortable kenneling facilities where their dogs will receive the recuperative care that they need, as well as the potentially life-saving treatment.
"The Charitable Trust has given millions of pounds to projects which help to improve the health and welfare of dogs across the UK. This unit has established the University's place as a leader in conducting not only lifesaving but also life enhancing work for dogs, and the Trust exists precisely to help projects such as this realise their goals."
The canine oncology support ward replaces the old feline ward, and the cats have been moved to a new ward further away from the dogs to help prevent cats from becoming stressed by the noise of barking.
Professor Elaine Watson, Head of the Royal (Dick) School of Veterinary Studies said: "The dog ward, along with our new feline ward enhances the facilities for animals receiving treatment at the School's Hospital for Small Animals and we are very appreciative of the tremendous support from the Kennel Club Charitable Trust."
Royal (Dick) School of Veterinary Studies at the University of Edinburgh has opened an emergency clinic for injured animals, to allow the public to bring in wildlife in need of treatment. The Wildlife Emergency Clinic is the first of its kind in the UK.
The new emergency clinic, based at the School's Hospital for Small Animals, will treat animals with the aim of releasing them back into their native habitat. The venture will also enable veterinary students to gain more hands-on training in treating wildlife.
The emergency clinic will treat animals, such as hedgehogs or injured birds, as well as larger animals such as deer. However, people are advised to contact the SSPCA to arrange for an inspector to be sent out for support if they have found a larger injured animal or if an animal seems in too much distress to be transported.
Emma Keeble, a wildlife veterinary expert at the Hospital for Small Animals, said: "At this time of year there may be orphaned hedgehogs found out during the day time, which are not able to fend for themselves or hedgehogs suffering from conditions such as fly-strike. As summer progresses there tend to be lawnmower and strimmer injuries. There are also other animals that may have been injured as a result of road accidents."
The School's Hospital for Small Animals already has an exotic and wildlife ward and works with the SSPCA to treat animals so that they can be released back into their native habitat.