Review provides important insights into the diagnosis of strangles

A recent study from the Royal Veterinary College (RVC), analysing laboratory diagnoses of strangles across the UK, has been published in the Veterinary Record. It paves the way for an improved understanding of the spread and control of strangles to reduce the impact of this devastating disease.

Strangles is a contagious upper respiratory tract infection, caused by the bacterium Streptococcus equi, which can affect horses, ponies and donkeys of any age, breed or sex with younger horses typically more severely affected. It is also one of the most prevalent infectious diseases amongst horses and ponies worldwide, carrying a very high welfare burden with up to 100% of horses in outbreaks becoming affected.

This landmark study, funded by The Horse Trust, brought together an international team from the RVC, the University of Melbourne, JDATA, Intervacc AB, Wellcome Trust Sanger Institute and the British Horseracing Authority. Researchers analysed data from seven UK diagnostic laboratories between January 2015 and December 2019, finding that 1,617 laboratory diagnoses of strangles were recorded over the study period. However, when taking into account the number of potentially undiagnosed horses, the true number of equids affected by strangles is thought to be much higher.

Importantly, the findings of this study begin to quantify the occurrence of strangles within the UK and guide veterinary surgeons in their approach to disease diagnosis. This includes not ruling out a strangles diagnosis when a horse or pony presents with more general clinical signs of nasal discharge, with or without fever, in the absence of abscessation or swelling of the submandibular and retropharyngeal lymph nodes. More generally, the study suggested that the description of ‘classical’ and ‘atypical’ clinical signs should be revised.

The study also provides a crucial resource for horse owners in the form of an online tool (www.jdata.co.za/ses) to identify if strangles outbreaks have occurred in their area, or a region they may be travelling to with their horses. This resource is actively updated meaning that if a region is currently experiencing higher numbers of strangles diagnoses, owners can stay informed and subsequently heighten their biosecurity and hygiene protocols. This will help to reduce the spread of strangles and ultimately the impact it can have on yards, owners and horses. The publication also reinforces the benefit of a united front for strangles research and how through laboratories, veterinary practices and owners working together, we can provide much more detailed insights into the disease, leading towards safeguarding the health of our horses.

Abigail McGlennon, PhD student in the Department of Pathobiology and Population Sciences, Royal Veterinary College, said:

“Prior to the development of the Surveillance of Equine Strangles network in 2018, there was limited information available about strangles diagnoses in the UK. This publication highlights the prevalence of strangles in the UK and the variation in signs that infected horses show. The results of this five year surveillance study enable the continued development of evidence-based recommendations within the equine industry to help reduce the spread of strangles and keep our horses healthy and happy.”

Nic de Brauwere Senior Welfare Veterinary Surgeon at Redwings, said:

“This welcome paper clearly shows how SES is making a huge additional contribution to our understanding of when, where and how strangles is circulating in the UK at any given time. It expands research beyond the labs and into the communities that are being affected by outbreaks, giving us essential, practical insights, such as the value of diagnostic tests in helping to identify strangles cases in all their forms, and the increased outbreak risk on commercial equine premises. We are glad to have SES and the RVC as collaborators for Strangles Awareness Campaign 2022 where research outputs help each SAW to be up to date and responding to the every changing picture of strangles in the UK”

Jan Rogers, Director of Research & Policy at The Horse Trust, said:

“The Horse Trust is delighted to have enabled this research, carried out by the combined expertise of the scientists involved, which has enabled the foundation of a surveillance network and highlighted key factors which can quickly be acted on by owners in order to be able to identify strangles and reduce the spread of this horrible disease. The work of these scientists fundamentally underpins the need for equine identification to become digitally based to enable accurate disease surveillance in the interests of horse wellbeing.