Streptococcal Pharyngitis

Streptococcus pyogenes attaches to epithelial cells using surface proteins, particularly lipoteichoic acid and M protein. The M protein promotes robust attachment to host tissue while inhibiting complement activation and opsonization, which impedes immune detection and phagocytosis. This dual mechanism ensures the bacterium establishes a foothold in the pharynx.

The hyaluronic acid capsule mimics host connective tissue, allowing the bacterium to evade immune recognition. This molecular camouflage is a key virulence factor that helps Streptococcus pyogenes avoid detection by the immune system and establish persistent infection in the pharynx.

Streptolysins O and S form pores in cell membranes of erythrocytes and leukocytes, causing cell lysis and tissue damage. Hyaluronidase cleaves hyaluronic acid in the extracellular matrix, increasing tissue permeability. Together, these enzymes degrade host defenses and facilitate bacterial penetration into deeper tissues.

The host initially confines infection by forming fibrin clots around bacteria. Streptokinase converts plasminogen into plasmin, which degrades fibrin clots and enables further bacterial spread. This virulence factor overcomes a critical host hemostatic defense, allowing the pathogen to disseminate beyond localized confinement.

Symptoms typically begin two to five days after exposure and include sore throat, fever, headache, and tender cervical lymphadenopathy. Physical findings often include erythema, edema, and purulent exudates or white patches on the tonsillar pillars and pharyngeal walls, reflecting the vigorous inflammatory response triggered by bacterial virulence factors.

Streptococcal pharyngitis spreads through respiratory droplets expelled during coughing, sneezing, or talking. Once inhaled, Streptococcus pyogenes enters the host and adheres to mucosal epithelial cells of the pharynx, initiating infection. This airborne transmission route makes strep throat highly contagious in close-contact settings.

Untreated streptococcal pharyngitis can lead to serious complications including rheumatic fever and post-streptococcal glomerulonephritis. In some cases, superantigens such as streptococcal pyrogenic exotoxins provoke systemic responses, contributing to complications like scarlet fever. Timely diagnosis and treatment help prevent these sequelae and complications similar to bacterial meningitis.