Globetrotting strangles: the unbridled national and international transmission of <i>Streptococcus equi</i> between horses
Journal: Equine Veterinary Journal
Summary
Strangles remains one of the most prevalent infectious diseases in horses globally, yet its epidemiological significance is underestimated at international policy level, partly because approximately 10% of recovered animals become asymptomatic carriers capable of transmitting *Streptococcus equi* to naive populations without detection during standard pre-purchase or transit examinations. Researchers analysed 670 *S. equi* isolates from 19 countries using core-genome multilocus sequence typing (cgMLST) to map genetic relationships and transmission pathways at high resolution, revealing distinct clusters and patterns of national and international disease spread. The phylogenomic analysis demonstrated multiple independent transnational transmission events, indicating that strangles circulates as a genuine international problem rather than isolated endemic pockets, with carrier animals serving as the primary mechanism for geographical dissemination. These findings underscore the need for heightened awareness among equine professionals regarding the disease's true economic and welfare burden, alongside the practical importance of identifying persistently infected animals before movement and implementing rigorous screening protocols at yards receiving travelling horses. The publicly accessible cgMLST web bioresource developed through this research provides farriers, veterinarians and other equine practitioners with a genomic tool to support investigation of strangles outbreaks within their local and national populations.
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Practical Takeaways
- •Implement rigorous screening protocols for carrier animals during pre-purchase and transit, as asymptomatic horses can transmit strangles across national borders
- •Recognize that strangles has significant international health, welfare and economic costs warranting disease surveillance and control at international level
- •Use genomic analysis tools to track S. equi transmission patterns and identify outbreak sources within and between horse populations
Key Findings
- •Analysis of 670 S. equi isolates from 19 countries identified national and international transmission events driving endemic disease
- •Approximately 10% of horses recovering from acute strangles develop persistent infection as asymptomatic carriers
- •Carrier animals appear clinically healthy and are rarely detected during routine pre-purchase or transit examinations, enabling disease transmission