Major study tracks Strangles prevalence in British horses

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A two-year-old Shetland pony (not involved in the study) with strangles.
A two-year-old Shetland pony with strangles. His first symptom was a runny nose. Then he developed a fever, and swelling to the right side of his face. © AkaEmma at English Wikipedia, Public domain, via Wikimedia Commons

A new study from the Royal Veterinary College (RVC), analysing laboratory diagnoses of strangles across the UK, paves the way for an improved understanding of the spread and control of strangles to reduce the impact of the 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.

The results of the study have been reported in the journal Veterinary Record. The study, funded by The Horse Trust with support from South Essex Insurance Brokers, 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 1617 laboratory diagnoses of strangles were recorded during that time. However, considering 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 valuable resource for UK horse owners in the form of SES (Surveillance of Equine Strangles) an online tool 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 – so 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, there can be more detailed insights into the disease, leading towards safeguarding the health of horses.

Owners can check online to see if strangles outbreaks have occurred in their area.
Owners can check online to see if strangles outbreaks have occurred in their area.

Lead author Abigail McGlennon, PhD student in the Department of Pathobiology and Population Sciences, Royal Veterinary College, said that before 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.”

Surveillance of strangles in UK horses between 2015 and 2019 based on laboratory detection of Streptococcus equi.
McGlennon A, Waller A, Verheyen K, Slater J, Grewar J, Aanensen D, Newton R.
Vet Rec. 2021;e948. https://doi.org/10.1002/vetr.948

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