Molecular characterisation of 'strangles' outbreaks in the UK: the use of M-protein typing of Streptococcus equi ssp. equi.
Authors: Ivens P A S, Matthews D, Webb K, Newton J R, Steward K, Waller A S, Robinson C, Slater J D
Journal: Equine veterinary journal
Summary
# Strangles Epidemiology Through M-protein Typing: Understanding Disease Spread in UK Horses Strangles remains the most significant infectious disease affecting horses globally, yet its outbreak patterns and transmission routes remain poorly characterised in the UK, where the disease is not notifiable. Researchers sequenced the variable region of the SeM gene (encoding a surface M-protein) from 145 *Streptococcus equi* isolates submitted by veterinary practices across the UK, identifying the different alleles present and mapping their geographic distribution using phylogenetic analysis. Twenty-one distinct SeM alleles were identified—including nine previously unknown variants—clustered into four phylogenetic groups, with alleles 9 and 7 predominating; notably, the data revealed a distinct outbreak cluster in the north-west of England, suggesting geographic specificity of certain strains. SeM typing demonstrates that individual strangles outbreaks can be differentiated and linked based on molecular signatures, revealing evidence of mutation driving emergence of novel but related variants in specific regions. For practitioners involved in outbreak investigation and control, this typing method offers a practical tool for determining whether apparently separate strangles cases represent linked transmission chains or independent introductions—information critical for implementing targeted biosecurity measures and understanding disease epidemiology at both regional and national levels.
Read the full abstract on PubMed
Practical Takeaways
- •Practitioners can use SeM typing to determine if strangles cases in their practice are connected to known outbreak strains or represent new introductions
- •Identifying outbreak clusters geographically may help target biosecurity measures and control strategies to high-risk regions
- •This molecular typing method enables better disease surveillance and can support evidence-based decisions about quarantine and movement restrictions during outbreaks
Key Findings
- •SeM gene typing identified 21 different alleles from 145 S. equi isolates, including 9 previously unidentified alleles grouped into 4 phylogenetic clusters
- •SeM alleles 9 and 7 were the most commonly isolated, with a high frequency of low-frequency alleles present
- •Geographic clustering was observed, with a notable outbreak cluster identified in the north-west UK
- •SeM gene sequencing is a useful epidemiological tool for differentiating and linking strangles outbreaks at regional, national, and international levels