Question
Non-suppurative diseases of streptococcus pyogenes
Answer
Non-suppurative complications of Streptococcus pyogenes (Group A Streptococcus) infection are immune-mediated delayed sequelae, occurring after the primary infection has often already resolved, rather than resulting from direct bacterial invasion:
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Acute rheumatic fever — follows streptococcal pharyngitis, occurring 2–4 weeks later; caused by molecular mimicry, where antibodies against streptococcal M protein cross-react with cardiac myosin/valve tissue, causing carditis (with potential long-term valvular damage), migratory polyarthritis, Sydenham’s chorea, subcutaneous nodules, and erythema marginatum.
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Acute post-streptococcal glomerulonephritis (PSGN) — can follow either pharyngitis or skin infection (impetigo), typically 1–3 weeks (pharyngitis) or 3–6 weeks (skin infection) later; caused by deposition of circulating immune complexes in the glomerular basement membrane, triggering complement activation and glomerular inflammation, presenting with haematuria, oedema, and hypertension.
Both are driven by the host’s immune response to the organism (molecular mimicry and immune-complex deposition respectively), rather than by ongoing bacterial presence at the affected organ — explaining why they can appear even after the original infection has clinically resolved.