Novel seM-types of Streptococcus equi subsp. equi identified in isolates circulating in Argentina.
Authors: Bustos Carla P, Muñoz Alejandra J, Guida Nora, Waller Andrew, Mesplet María
Journal: Equine veterinary journal
Summary
# Strangles in Argentina: Emerging strain diversity and regional epidemiology Strangles, caused by *Streptococcus equi* subsp. *equi*, remains a significant respiratory disease in horses worldwide, and seM-typing provides a standardised molecular tool for tracking strain distribution and outbreak patterns across populations. This Argentinian investigation characterised 59 isolates collected over a 12-year period (2007–2019) using seM-typing alongside phylogenetic analysis and amino acid sequencing to establish the circulating strain landscape. Eight distinct seM-types were identified, comprising just one previously documented variant (seM-61) and seven novel alleles (seM-129 through seM-135), with notably high genetic homology observed between most Argentinian strains—except seM-130—and close relatedness to Brazilian isolates, suggesting geographical restriction of strain distribution linked to horse movement between disciplines and bordering countries. The lack of predicted functional consequences from identified amino acid differences indicates these variants are likely epidemiologically distinct rather than functionally divergent, making them valuable epidemiological markers rather than indicators of altered virulence or clinical presentation. For practitioners, these findings underscore the value of molecular strain typing in outbreak investigation and disease control strategies, particularly when managing strangles in populations with cross-border horse movement, and support the utility of seM-typing databases for distinguishing unrelated incursions from recirculating endemic strains within regional equine populations.
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Practical Takeaways
- •Strangles strains circulating in Argentina show distinct geographical patterns with limited genetic diversity; understanding local strain types helps with disease management and epidemiological tracking
- •The presence of multiple novel seM-types indicates active transmission and evolution of S. equi subsp. equi in Argentine horse populations, requiring ongoing surveillance
- •Horse movement between countries and equine disciplines appears to be the primary mechanism for strain distribution, suggesting biosecurity protocols should consider regional strain patterns
Key Findings
- •Seven novel seM-types (seM-129, seM-130, seM-131, seM-132, seM-133, seM-134, seM-135) were identified in Argentine isolates, with only seM-61 previously reported
- •High genetic similarity observed among Argentine seM-types except seM-130, suggesting geographical clustering of strain types
- •SeM-61 was previously reported in Brazil, indicating regional strain distribution between neighbouring countries