Characterization of a mucoid clone of Streptococcus zooepidemicus from an epizootic of equine respiratory disease in New Caledonia.
Authors: Velineni Sridhar, Desoutter Denise, Perchec Anne-Marie, Timoney John F
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Streptococcus zooepidemicus normally colonises healthy horses as a commensal organism but can cause opportunistic lower respiratory tract infections when immune defences are compromised by viral co-infection, stress, or environmental factors; this outbreak investigation examined an unusual mucoid clone that spread across multiple locations in New Caledonia, challenging the typical pattern of strain variation between individual animals. Researchers isolated the mucoid strain (SzNC, ST-307) from transtracheal aspirates and 80% of nasal swabs from affected horses (n=31), compared to only 4% prevalence in unaffected horses (n=25), and confirmed clonality through colony morphology, protein sequencing, and multilocus sequence typing. The outbreak strain possessed distinct surface proteins—notably DnaK and alanyl-tRNA synthetase—that were absent from non-clonal strains and demonstrated strong reactivity with convalescent serum, indicating these were expressed during active infection and recognised by host immune responses. This stable mucoid phenotype with specific virulence-associated protein markers suggests SzNC possessed enhanced transmissibility or pathogenic potential compared to typical invasive strains, though a viral trigger was ruled out through serological screening. For practitioners, this work underscores that whilst S. zooepidemicus respiratory disease is usually sporadic and individual, clustering of cases warrants investigation for atypical clonal variants that may require adjusted outbreak management strategies and closer biosecurity measures than conventional opportunistic infections.
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Practical Takeaways
- •A novel mucoid strain of S. zooepidemicus was responsible for a multi-site respiratory disease outbreak in New Caledonian horses, suggesting heightened transmissibility or virulence compared to typical non-mucoid strains
- •Respiratory disease in horses should prompt investigation for S. zooepidemicus as a secondary bacterial pathogen, particularly when viral causes are ruled out
- •The identification of this clonal strain and its unique surface protein profile may inform development of targeted diagnostics and potential vaccine strategies for preventing opportunistic S. zooepidemicus infections
Key Findings
- •A novel stably mucoid clone of S. zooepidemicus (SzNC, ST-307) caused a clonal epizootic of respiratory disease in horses across multiple locations in New Caledonia
- •SzNC was isolated from 80% of nasal swabs (n=31) from affected horses compared to only 4% from unaffected horses (n=25)
- •The clonal isolate expressed unusual surface proteins (DnaK and AlaS) and SzP with N2 terminal and HV4 variable region motifs not found in non-clonal strains
- •Most SzNC isolates were hyaluronidase positive and demonstrated reactivity with convalescent serum, indicating active expression during infection