Streptococcal infection complications

Mechanisms of complication development

The primary cause of severe systemic consequences is the ability of group A beta-hemolytic Streptococcus (GAS) to evade the immune system. This phenomenon is called molecular mimicry. Bacterial antigens (M-protein, streptokinase, A-polysaccharide) are structurally similar to the sarcolemma of cardiac myofibrils and renal tissue. As a result, antibodies produced against the infection begin to attack the body's own organs.

Additionally, GAS possesses high invasiveness: it is capable not only of adhering to cells, but also of penetrating into the cytoplasm and then into the nucleus, lysing the area around the nucleolus. Chronic progression and recurrences are often associated with the transition of the bacteria into L-forms, which can persist in the body for long periods. Epidemic outbreaks of the disease are often explained by mutations in emm genes encoding the M protein.

Early (purulent) complications

Arise due to direct spread of the pathogen from the primary focus (pharynx or tonsils) to adjacent tissues or via the bloodstream. Caused by the septic component of pathogenesis.

• Involvement of fascial spaces: peritonsillar and retropharyngeal abscesses, parapharyngitis. With progression, pus can track downwards through fascial planes, causing cervical phlegmon and severe purulent mediastinitis.
• ENT complications: otitis media, sinusitis, mastoiditis (when the infection spreads to the paranasal sinuses and middle ear).
• Lymphatic system: purulent or necrotic lymphadenitis of regional cervical nodes, adenophlegmon.
• Generalization (septicopyemia): formation of metastatic abscesses in internal organs and development of purulent meningitis (most commonly via contiguous spread from the ear or sinuses).

Late (autoimmune) complications

Develop on the 2nd–3rd week after tonsillitis or scarlet fever against the background of pronounced body sensitization.

• Acute rheumatic fever (rheumatism): caused by specific rheumatogenic M-serotypes (e.g., 1, 3, 5, 6, 14, 18, 19, 24). Manifests as rheumatic endocarditis and myocarditis (coming to the foreground 5–7 days after joint syndrome subsides), migratory polyarthritis of large symmetrical joints (with a predominance of exudation and healing without severe deformities), polyserositis, and rheumatic pneumonia. The morphological basis of disease activity consists of specific rheumatic granulomas, as well as nonspecific exudative reactions and vasculitis in the microvasculature.
• Acute post-streptococcal glomerulonephritis: triggered by specific nephritogenic strains. Unlike rheumatic fever, an immune complex mechanism is at play here—antigen-antibody complexes deposit on the basement membrane of renal glomeruli due to cross-reactivity, causing proliferative inflammation.

Virulence factors and laboratory diagnostics

Host tissue damage is mediated by potent GAS enzymes and toxins:

• Cell wall M-protein is the main virulence factor that inhibits phagocytosis by macrophages.
• Pneumolysin — damages target cell membranes.
• Streptolysins O and S — activate the conversion of plasminogen to streptokinase, leading to plasmin generation and fibrinolysis.
• C5a peptidase — destroys the chemotactic factor.
• Hyaluronidase — facilitates bacterial movement through connective tissue.

To confirm the streptococcal nature of complications, throat swab bacteriological culture for group A Streptococcus and serological tests are used. The combination of an elevated ASO (antistreptolysin O) titer with anti-DNase B or antihyaluronidase has the highest diagnostic sensitivity.

Class and exam questions

What else to study on this topic

• Epidemiology and transmission routes of streptococcal infection.
• GAS virulence factors and their impact on the immune response.
• Clinical presentation of acute rheumatic fever.
• Pathomorphology of rheumatic granulomas and vasculitis.
• Mechanisms of streptococcal L-form formation and chronicity of the process.

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