Unwelcome neighbours: Tracking the transmission of Streptococcus equi in the United Kingdom horse population.
Authors: McGlennon Abigail A, Verheyen Kristien L, Newton J Richard, van Tonder Andries, Wilson Hayley, Parkhill Julian, de Brauwere Nicolas, Frosth Sara, Waller Andrew S
Journal: Equine veterinary journal
Summary
# Editorial Summary: Genomic Tracking of Strangles Transmission in UK Horse Populations Strangles remains endemic across the UK with approximately 300 laboratory diagnoses annually, yet the relative contribution of acutely infected horses versus sub-clinical carriers to ongoing transmission has remained unclear. Researchers analysed whole-genome sequences from 511 *Streptococcus equi* isolates collected between 2015 and 2022, reconstructing a dated phylogenetic tree and using Bayesian clustering and transmission modelling to map population structure and identify likely transmission pairs. Two dominant genetic groups accounted for 82% of circulating strains, with McG-BAPS3 increasing significantly in prevalence whilst McG-BAPS5 declined over the study period—a pattern suggesting active, dynamic transmission rather than static carrier reservoirs. The analysis identified 16 direct transmission pairs, including 10 between horses from different UK regions, and reconstructed a transmission chain spanning six months across nine horses, indicating that acutely infected and recently convalesced short-term carriers likely drive endemic persistence more substantially than long-term carriers. These findings have important implications for biosecurity protocols and disease management strategies: rather than focusing exclusively on identifying persistent carriers, practitioners should prioritise early detection and isolation of acutely affected horses and implement regional surveillance networks, as real-time genomic tracking could enable rapid identification of emerging transmission clusters and inform targeted interventions before wider spread occurs.
Read the full abstract on PubMed
Practical Takeaways
- •Strangles transmission in the UK is driven primarily by acutely infected or recently recovered horses rather than long-term carriers—focus biosecurity and isolation protocols on horses showing active or recent clinical signs
- •Transmission occurs readily across different UK regions, suggesting the pathogen circulates widely; consider that purchased or transported horses may introduce new strains to your facility regardless of apparent health status
- •A real-time genomic surveillance system could enable faster identification of transmission clusters and allow targeted interventions; work with your veterinarian to support such surveillance initiatives and ensure rapid reporting of cases
Key Findings
- •82% of S. equi strains clustered into two BAPS groups (McG-BAPS3 and McG-BAPS5), with McG-BAPS3 increasing and McG-BAPS5 decreasing in prevalence over 2015-2022
- •Sixteen direct transmission pairs were identified, with 10 occurring between horses from different UK regions, indicating regional transmission
- •A transmission chain was inferred extending over 6 months involving nine horses, with 64% of sequenced isolates (286/447) included in eight identifiable transmission clusters
- •Acutely infected and recently convalesced short-term carrier horses appear to play a more influential role in transmission than long-term carriers based on rapid population structure changes