Science in brief: Equine Infectious Disease and Microbiology is edited by Julia Kydd and Celia Marr with guest editors Macarena Sanz, Tessa LeCuyer and Laura Peachey.
The issue groups papers around national disease surveillance, the need for definitive diagnosis in some infections, and cross-species comparisons for pathogens affecting multiple species.
Diagnostics papers cover techniques for equine fever, equine influenza and equine gastrointestinal parasites, with the editors noting these developments should help speed biosecurity implementation to limit transmission.
Gastrointestinal papers include metabolic profiling for earlier insights into equine proliferative disease in foals, potential colitis aetiology, and the importance of additional testing for chronic hepatitis and liver failure in hepacivirus cases.
Two antimicrobial papers address resistance, one suggesting that prophylaxis beyond 24 hours is unnecessary to prevent post-surgical complications after colic surgery.
Respiratory studies include multiple strangles papers concluding prevention needs thorough screening, consistent quarantine, close monitoring and interconnected reporting.
The section also includes a special collection on the equine microbiome, updating EVJ’s 2019 collection and flagging progress over the past seven years.
Julia Kydd said: “The considerable and diverse research efforts within this Special Focus will ultimately improve the detection, diagnosis, treatment and control of many pathogens.
“The eventual aim is to prevent or minimise the impact of future outbreaks.”
https://beva.onlinelibrary.wiley.com/toc/20423306/2026/58/2
The collection, which is free to read until 7th January 2026, explores:
Laura Nath said: “This collection highlights important and exciting work and improves our understanding of arrhythmogenic mechanisms, diagnosis of arrhythmias and recognition of cardiac pathology in both clinical and research settings.”
https://beva.onlinelibrary.wiley.com/doi/toc/10.1001/(ISSN)2042-3306.current-progress-in-equine-cardiology
The article argues that as the equine influenza (EI) vaccine supply returns to normal, there is sound scientific evidence why bi-annual vaccination schedules should be re-implemented promptly.
Whilst the scale and number of outbreaks has been relatively small since the introduction of mandatory EI vaccination by most competitive equestrian disciplines in the 1980s, disease events such as those experienced in the UK in 1989, 2003 and most recently in 2019 have demonstrated EI’s epidemic potential, even in vaccinated horse populations.
In their article 'Equine influenza bi-annual boosters: what does the evidence tell us?' Victoria Colgate and Richard Newton discuss what has been learnt from previous outbreaks and explain the evidence from mathematical models to show why bi-annual boosters are beneficial.
The authors say that epidemiological data from previous natural EI outbreaks have repeatedly demonstrated the impermanent nature of the protection provided by vaccination and observational field studies have repeatedly highlighted the potential for 12-monthly boosters to leave a vulnerable immunity gap at both the individual animal and population level.
Mathematical models of EI transmission confirm that six-monthly rather than annual EI booster vaccinations are preferable to establish and maintain effective population level immunity to EI.
Ideally vaccine strains should be updated in a timely manner to ensure inclusion of the most epidemiologically-relevant strains, however, this is a slow and expensive process for equine vaccine manufacturers.
In the absence of updated vaccine strains, bi-annual vaccination is strongly recommended to help compensate for antigenic drift between vaccine and circulating EI viral strains
Professor Celia Marr, Editor of the EVJ said: “Although the recent EI vaccine shortage has necessitated a temporary relaxation of competition vaccine schedules, we must now renew the message that six-monthly boosters are optimal and necessary.”
The Editorial can be found at https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.13898 and is free to view.
Two related articles can be found here: https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.13874 and here: https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.13885
Until now, research in equine veterinary science has focused primarily on the information needed to prevent and cure disease, with little attention paid to the attitudes and actions of horse owners, veterinary surgeons, and numerous other professionals to implementing science-based advice.
This special EVJ collection showcases studies that seek to understand horse owner behaviour around their horse’s health, supplementing clinical evidence with information about the real-life behaviours of equine owners and professionals and the factors that influence them.
It includes papers on horse owner knowledge and opinions on recognising colic, treating infectious disease, uptake of some of the most basic preventive health measures such as vaccination and deworming as well as attitudes and behaviour around equine obesity and laminitis.
Other studies highlight the importance of professionals other than vets such as farriers, equine podiatrists, physiotherapists, dental technicians, chiropractors, and equestrian organisations such as the British Horse Society.
Guest Editor Tamzin Furtado added: “As our understanding of the drivers of behaviour develops, pre-existing behaviour change models will help us to understand the barriers and enablers to uptake.
“With dissemination of this knowledge, we have a better chance of communicating effectively and implementing change that will have a positive impact on equine welfare at individual, community, and national level.”
Professor Celia Marr, Editor of the EVJ said: “This collection is both compelling and eye-opening.
"It is dangerous to assume an understanding of the motivators of horse owner behaviours and actions; these papers confirm the current lack of comprehension, providing an invaluable insight, which will ultimately help us to accelerate improvements in equine veterinary practice and, most importantly, equine welfare.”
The virtual issue can be found at https://beva.onlinelibrary.wiley.com/doi/toc/10.1001/(ISSN)2042-3306.owner-behaviours and will be free to view until 26 December 2022.
Omics refers to a field of biological sciences including genomics (studying DNA), transcriptomics (RNA), proteomics (proteins) and metabolomics (metabolites).
Guest Editor Carrie Finno has contributed an editorial in support of the nine EVJ articles demonstrating how genomic and transcriptomic approaches have been used to investigate equine diseases.
She said: “While equine genomics and transcriptomics continue to evolve, improvements in the annotation of the equine genome will undoubtedly accelerate the rate of discovery.
"With the need for large sample sizes of well-phenotyped horses to study the most complex diseases, equine genomics and transcriptomics research will likely become increasingly collaborative, similar to the current status of human genomics initiatives.
"Aligned with this collaborative effort is the strong need for publicly available genomic and transcriptomic data that are accessible to all researchers.”
Guest Editor James Anderson prefaces five papers on advances made in equine medicine within the disciplines of proteomics, metabolomics and lipidomics (a subset of metabolomics).
He said: “Omics technologies have enhanced our knowledge of the molecular world and provided fascinating insight into the composition and functions of these components across a range of different animal species.
"Particularly for equine science and medicine they have increased our understanding of molecular changes in disease and informed the development of diagnostic tests.
"Although still in its infancy within equine veterinary science, this field looks likely to have a significant impact in the coming years.”
The virtual Issue is available to all at https://beva.onlinelibrary.wiley.com/doi/toc/10.1001/(ISSN)2042-3306.OmicsEVJ
The virtual collection provides a source of evidence to determine what is or is not of clinical significance in cardiac arrhythmia and what might represent the best course of action, if action is needed, within the requisite parameters of safety and welfare.
With an editorial written jointly by Peter Physick-Sheard and Joann Slack the virtual collection includes:
... and more.
Professor Celia Marr, Editor of the EVJ said: “In terms of day-to-day veterinary work, rhythm disturbances are a frequent frustration during prepurchase examinations or perceived poor performance assessments. This outstanding collection brings to hand the most recent evidence to help clinicians support their observations, facilitating diagnosis and a treatment plan in this challenging area.”
The Virtual issue can be downloaded here: https://beva.onlinelibrary.wiley.com/doi/toc/10.1111/(ISSN)2042-3306.irregular-hearts-performance.vi
Until the arrival of Computed Tomography (CT) and Magnetic Resonance Imaging (MRI), radiographs were the only feasible option. More recently, the availability of bigger, wider and more adaptable scanners has allowed horses to be examined in a standing position, significantly improving diagnostic and treatment strategies and avoiding the need for general anaesthetic.
Against this background the collection considers the advantages of cutting-edge modalities and draws comparisons with more readily available tools such as radiography.
Given the increase in use of CT in horses and the contamination hazards faced particularly by horse handlers, two practical articles in the collection describe the role of equine head CT, how to set up standing equine CT and the radiation exposure risks.1,2
The most revolutionary recent advance in diagnostic imaging for dental disease in horses is CT. However, a study of horses with diseased mandibular cheek teeth found that while CT is useful to identify defects in the bone and tooth it is far less useful for the identification of inflammation and tissue destruction which is far better served by MRI.3
The structure of the equine head is complex and subject to great variation so several articles focus on practical anatomy and interpretation of radiographs of this region.4.5 Advanced diagnostic techniques are helping with clinical and surgical approaches to problems with the equine head. The sphenopalatine sinus is challenging to assess radiographically because of its tricky position but CT can help overcome this obstacle. One of the studies describes how CT can help unravel the pathology of various equine sinonasal tumours. Other articles cover less common pathological conditions including the historical, clinical, diagnostic imaging findings and outcomes of five horses with pneumocephalus. 6,7,8
Practitioners recognise MRI as the gold standard for neurologic imaging because of the excellent soft tissue detail but the size of horses and the size of scanners makes it a challenge to use. An additional constraint is the longer acquisition time compared to CT. Notwithstanding these limitations three studies in the collection display the various benefits of using MRI for the spine and neck, including the evaluation of 84 equine head disorders, the diagnosis of cervical stenotic myelopathy, and the assessment of two foals with closed head trauma.9,10,11,12
Despite the significant advances in imaging, the horse’s back is still defying conventional systems, primarily because of its size, concludes a spinal evaluation article. New technologies such as robotic fluoroscopy and cone-beam CT, may provide a cross-sectional method to evaluate the equine spine, but for now radiographs are still better to help evaluate findings of spinous process impingement seen on scintigraphy. The take home message here is that the wide variety of abnormalities seen on scintigraphy and radiography in horses with and without back pain makes a diagnosis more likely to be achieved by physical examination rather than the imaging findings.13
Anthony Pease, associate editor of the EVJ said: "Advanced imaging is still in its infancy with sequences still being developed to help optimise the time and detail needed for diagnosing complex musculoskeletal and neurologic disorders. Continued research in a controlled environment and comparing to histopathology will allow clinicians to further their knowledge and understanding of the CT and MRI findings in the equine patients."
References
Four separate studies are included in the collection, reporting novel risk factors for the disease, identifying key differences between EGS and botulism (questioning the hypothesis that EGS is caused by neurotoxins from Clostridium botulinum), reporting a novel diagnostic technique and showing the value of monitoring weight loss to help predict whether individual horses with chronic EGS are likely to survive.
The publishers say that despite more than 100 years of research, supported predominantly by the The Moredun Foundation Equine Grass Sickness Fund (www.grasssickness.org.uk), the cause of EGS remains unknown. Since it almost exclusively affects grazing horses, a pasture derived neurotoxin is implicated. EGS causes gut paralysis as a result of damage to parts of the nervous system that control involuntary functions. Acute and sub-acute EGS is invariably fatal while around 55% of chronic cases can survive and return to a useful working life. The UK has the highest incidence of EGS in the world; indeed it is estimated that the disease kills between 1 and 2% of horses in the United Kingdom annually. Cases are more common in spring.
In terms of risk factors, the study ‘Equine grass sickness in Scotland: A case-control study of environmental geochemical risk factors’ suggests that the high incidence of the disease in Eastern Scotland may be partly associated with the particular composition of macro and trace elements in the soil in the fields on which horses graze. Further work is required to determine whether interventions to alter concentrations of particular elements in soil could potentially reduce the risk of EGS.1
A second study identified key differences between EGS and botulism, which questions the currently favoured hypothesis that EGS is caused by neurotoxins from Clostridium botulinum, a bacterium which commonly inhabits soil. The study ‘Equine grass sickness, but not botulism, causes autonomic and enteric neurodegeneration and increases soluble N-ethylmaleimide-sensitive factor attachment receptor protein expression within neuronal perikarya’ suggests that EGS is unlikely to be caused by neurotoxins from this bacterium and concludes that further investigation of an alternative cause for EGS is needed.2
While the majority of horses with EGS can be readily diagnosed by experienced veterinary surgeons, some cases present a diagnostic challenge. Indeed the only way to definitively diagnose the disease in a live horse is to demonstrate the characteristic degeneration of nerves within biopsies of the intestine. Unfortunately these biopsies can only be collected by performing abdominal surgery under general anaesthesia. In the study ‘Neuronal chromatolysis in the subgemmal plexus of gustatory papillae in horses with grass sickness’ characteristic degeneration of nerves was identified in small biopsies collected from tongues of EGS horses during post mortem examination. Examination of these biopsies accurately differentiated control horses from EGS cases. While further validation of this technique is required, it could potentially provide a relatively non-invasive method of confirming the diagnosis in a live horse.3
While around 55% of horses with chronic EGS survive, objective criteria for predicting survival of these cases are currently lacking. The study ‘Bodyweight change aids prediction of survival in chronic equine grass sickness’ reported that non-survivors had greater rate and magnitude of bodyweight loss than survivors. Survival prediction curves were published to allow veterinary surgeons and horse owners to use body weight data to help determine whether an individual horse with chronic EGS was likely to survive or die.4
Professor Bruce McGorum, Head of the Equine Section at the Royal (Dick) School of Veterinary Studies & Roslin Institute in Edinburgh, has been leading much of the research. He said: "Given that our recent research suggests that EGS is unlikely to be caused by neurotoxins from Clostridium botulinum we are now moving on to determine whether EGS is caused by ingestion of mycotoxins produced by pasture fungi. We are very pleased that The Horse Trust (www.horsetrust.org.uk) has provided funding for this three-year investigation."
Professor Celia Marr, Editor of the Equine Veterinary Journal said: “While the cause of equine grass sickness continues to evade us, these papers present an optimistic step in the right direction for the eventual prevention of this dreadful disease. It is only with the support of the Moredun Foundation Equine Grass Sickness Fund and more recently that of The Horse Trust that our world-leading veterinary researchers are able to continue to unravel the mystery.”
The EVJ equine grass sickness collection can be downloaded at http://bit.ly/2dC7Drr
Co-edited by Paddy Dixon and Vicki Nicholls, the collection comprises ten studies on physiology, disease, diagnosis and treatment techniques in equine dentistry. The editors say it gives veterinary surgeons free access to some of the most important current research in the UK.
The studies include:
Professor Celia Marr, Editor of the Equine Veterinary Journal said: "Care of the horse’s teeth is fundamental to good health. To this end a strong working knowledge of equine dentistry should be seen as an essential cornerstone for every equine practitioner. This diverse collection has the convenience of being easily accessible, online and in one place to help keep vets fully abreast of the excellent research currently being conducted in the UK."
Vicki Nicholls, incoming president of BEVA, continued: "Advances in equine dentistry continue to gather pace and it has been a pleasure and privilege to work with Paddy Dixon collating the most current dental research that will be relevant to all equine practitioners with any level of expertise."
The equine dentistry collection is available free online at: http://bit.ly/2bBDuMW.
New research from the USA, published in the Equine Veterinary Journal (EVJ), has shown that a toxin from the box elder tree is the likely cause of Seasonal Pasture Myopathy (SPM), the US equivalent of the European disease known as Atypical Myopathy (AM).
According to the British Equine Veterinary Association, preliminary comparisons of these results with cases of AM in Europe suggest that the European condition may be linked to similar trees which could have an important bearing on the future prevention of the disease in Europe.
Seasonal Pasture Myopathy is a highly fatal muscle disease in Midwestern USA and Eastern Canada. A similar disorder called Atypical Myopathy is becoming increasingly frequent in the UK and Northern Europe. Outbreaks of both diseases tend to be seasonal, with most cases occurring in the autumn. Horses that develop SPM and AM are usually kept in sparse pastures with an accumulation of dead leaves dead wood and trees in or around the pasture and are often not fed any supplementary hay or feed.
The research1 identified that seeds from box elder trees were consistently present in the autumn pastures of all 12 horses enrolled in the study. These horses were from 11 different farms and had all presented with the clinical signs of SPM, which include muscular weakness and stiffness, dark urine, periods of recumbency, colic-like signs and muscle trembling. The toxic amino acid hypoglycin A, which is known to cause acquired multiple acyl CoA dehydrogenase deficiency (MADD) was shown to be present in the box elder seeds and hypoglycin metabolites were identified in the serum or urine of all the horses. All but one of the cases proved fatal.
Professor Valberg DVM PhD of the Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, who instigated the study, said: "The fact that another acquired form of MADD in rats and humans is caused by hypoglycin A ingestion strengthens our conclusion that hypoglycin A is the likely toxic cause of SPM in horses. We are intending to conduct further studies to determine the factors that affect the highly variable hypoglycin A concentrations in box elder seeds."
Professor Valberg has established collaborative links with groups in Europe in order to investigate if a similar toxin is involved in European Atypical Myopathy. Working with Professor Vince Gerber and Dr Lucia Unger at the University of Bern, Professor Valberg has obtained seeds from a tree related to the Box Elder found on many pastures where Atypical Myopathy has occurred.
Professor Celia Marr, Editor of Equine Veterinary Journal said: "This is a really important step forwards. We don't yet know for sure that the cause of European disease, Atypical Myopathy, is the same as Seasonal Pasture Myopathy in the US. But the clinical signs and MADD aberrations are identical and both conditions have a high fatality rate. It remains to be seen whether this research will help European horses, but there is no doubt that it will allow American horse owners to prevent this devastating condition affecting their horses with immediate effect."
1 Seasonal Pasture Myopathy/Atypical Myopathy in North America associated with Ingestion of Hypoglycin A within Seeds of the Box Elder Tree Stephanie J Valberg DVM PhD1, Beatrice T Sponseller Dr. med. vet2, Adrian D Hegeman PhD3, Jennifer Earing PhD, Jeffery B. Bender DVM MS1, Krishona L Martinson PhD4, Steven E Patterson PhD5, Lawrence Sweetman PhD1