Poster Presentation Lancefield International Symposium for Streptococci and Streptococcal Diseases 2025

Household molecular epidemiology of Streptococcus dysgalactiae subsp. equisimilis carriage and infection in The Gambia (#70)

Gabrielle de Crombrugghe 1 2 3 , Edwin P Armitage 3 4 5 , Alexander J Keeley 3 4 6 7 , Elina Senghore 3 , Fatoumata Camara 3 , Musukoi Jammeh 3 , Amat Bittaye 3 , Haddy Ceesay 3 , Isatou Ceesay 3 , Bunja Samateh 3 , Muhammed Manneh 3 , Gwenaëlle Botquin 2 , Dalila Lakhloufi 2 , Valerie Delforge 2 , Lionel Schiavolin 2 , Claire E Turner 6 8 , Michael Marks 4 9 10 , Thushan I de Silva 3 6 7 , Anne Botteaux 2 , Pierre R Smeesters 1 2 11 12
  1. Department of Paediatrics, Brussels University Hospital, Academic Children Hospital Queen Fabiola, Université Libre de Bruxelles, Brussels, Belgium
  2. Molecular Bacteriology Laboratory, European Plotkin Institute for Vaccinology, Université Libre de Bruxelles, Brussels, Belgium
  3. Vaccines and Immunity Theme, Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine, Banjul, The Gambia
  4. Department of Clinical Research, Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK
  5. Population Health Sciences, Bristol Medical School, University of Bristol, BS8 2PN, UK, Bristol
  6. Florey Institute of Infection, University of Sheffield, Sheffield, UK
  7. Division of Clinical Medicine, School of Medicine and Population Health, University of Sheffield, Sheffield, UK, Sheffield
  8. School of Biosciences, University of Sheffield, Sheffield, UK , Sheffield
  9. Hospital for Tropical Diseases, University College London Hospital, London, UK
  10. Division of Infection and Immunity, University College London, London, UK
  11. Tropical Diseases Research Group, Murdoch Children’s Research Institute, Melbourne, Victoria, Australia
  12. Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia

Background
Streptococcus dysgalactiae subsp. equisimilis (SDSE) is a human pathogen closely related to Streptococcus pyogenes, causing similar clinical manifestations. They both evolve in the human pharynx and skin, demonstrate interspecies gene transfer and extensive shared gene content. Most SDSE studies focus on invasive disease, with only few on non-invasive infections and carriage. Data from low- and middle-income countries are scarce, and no emm-typing data has been reported from Africa so far. 

Methods
A household cohort study was conducted in The Gambia between 2021 and 2022, recruiting 442 participants from 44 households. Throat and skin swabs were collected to assess carriage and non-invasive disease. Beta-haemolytic positive isolates underwent emm-typing.

Results
A total of 273 SDSE isolates were identified, describing 26 emm-types. Among population-based isolates, three emm-types predominated, accounting for 47.5% of isolates. SDSE emm-type diversity (SRI 13.8, 95% CI: 10.8–19.2) was significantly lower than that of S pyogenes in the same cohort (SRI 29.3, 95% CI: 24.8–36.0). Most isolates were collected from throat carriage (81.3%, 130/160), followed by pharyngitis (10.6%, 17/160), skin carriage (5.6%, 9/160), and pyoderma (2.5%, 4/160). Of the 18 globally predominant emm-types described worldwide, 10 were found in the Gambian cohort while the predominant European strain stG62647 was absent (1, 2). 

Conclusion
This study offers the first molecular analysis of SDSE carriage and non-invasive infection in Africa. Our data suggest that the throat is a critical reservoir in this rheumatic heart disease-endemic region. Further investigation into SDSE epidemiology and its relationship with S pyogenes is essential.

  1. Xie, O., Davies, M. R., & Tong, S. Y. (2024). Streptococcus dysgalactiae subsp. equisimilis infection and its intersection with Streptococcus pyogenes. Clinical Microbiology Reviews, e00175-23.
  2. Oppegaard, O., Mylvaganam, H., Skrede, S., Lindemann, P. C., & Kittang, B. R. (2017). Emergence of a Streptococcus dysgalactiae subspecies equisimilis stG62647-lineage associated with severe clinical manifestations. Scientific reports, 7(1), 7589.