28 Aug 2025
Contrary to previous understanding, researchers find short-term carriers play a larger role in transmission than long-term carriers.
Chris Simpson
Job Title
Image © Alexey Stiop / Adobe Stock
A new study into the transmission of strangles in the UK has “significantly” advanced understanding of how the equine disease spreads.
Researchers found that short-term carriers play a larger role in transmission than long-term carriers, contrary to previous understanding.
In light of the findings, they called on vet surgeons to promote outbreak management measures and post-infection screening protocols among affected horse owners.
The study also found evidence of transmission chains running throughout the UK, including one spanning England, Wales, Scotland and Northern Ireland, shedding new light on the contagious disease’s spread through horse movements.
The researchers analysed 511 strangles samples taken between 2015 and 2022 using genome sequencing and epidemiological data.
While long-term carriers – horses that passed the usual four-week convalescence period but were not fully clear of infection, thereby remaining infectious for months or years – were thought to be the main drivers of outbreaks, newer strains were found to be much more prevalent.
During the study period, rapidly accumulated year-on-year changes in the relative frequencies of an older and newer strain were noted, suggesting acutely infected horses or recently convalesced subclinical short-term carriers were more likely to be responsible for fresh outbreaks.
The scholars argued identifying long-term carriers – and employing post-infection screening and clearance measures to prevent animals becoming long-term carriers – remains crucial to limiting its spread, however.
Of the 16 direct transmission pairs identified, almost two-thirds (62.5 per cent) were between horses from different regions, with one chain spanning six months and all four UK nations.
While this was said to be not unexpected given the frequency with which horses are transported for pleasure, competition, sales or veterinary care, it highlighted how movement can facilitate the spread of disease and the need for preventive biosecurity measures, real-time screening and vaccination.
The authors are encouraging vets to work with owners to develop strangles management plans, including diagnostic confirmation and post-infection screening.
Co-author Nic de Brauwere said the findings “advanced our knowledge around strangles transmission significantly”.
He added: “It is so rewarding when high-level research is able to have real-world relevance and bring immediate potential benefits to equine health.
“Owners, yards and vets can improve how they focus their screening efforts on the highest risk situations based on sound evidence, making the best use of limited resources while having a direct impact on the spread of infection to new susceptible equines.”
Lead author Abigail McGlennon said: “This study shows how important enhanced surveillance utilising epidemiological and genomic data is to investigate and understand strangles transmission across the UK.
“Our data highlights the importance of greater awareness and adoption of post-outbreak screening protocols to confirm freedom from infection, rather than owners assuming recovery based on the resolution of clinical signs.”
Funded by The Horse Trust, the paper was published in the Equine Veterinary Journal by researchers from the RVC, University of Cambridge, Swedish University of Agricultural Sciences and Redwings Horse Sanctuary.
