## Pathogenesis of Enteric Fever **Key Point:** Rose spots are a characteristic but non-specific finding in enteric fever, but their pathogenesis is NOT direct endotoxin action. ### Rose Spots: True Mechanism Rose spots are small (2–3 mm), blanching, erythematous macules that appear on the trunk in ~5% of enteric fever cases. They represent: - Vasculitis of small dermal vessels - Result of immune complex deposition and inflammatory response, NOT direct endotoxin effect - Appear during the second week of illness - Fade within 3–4 days **Warning:** The distractor claims endotoxin *directly* causes rose spots — this is mechanistically incorrect. Endotoxin triggers systemic inflammation, but rose spots are a secondary vasculitic phenomenon. ### Correct Pathogenic Features (Options 0, 2, 3) | Feature | Mechanism | |---------|----------| | **Invasion via M cells** | Salmonella typhi crosses the intestinal epithelium through M cells in Peyer's patches; this is the portal of entry | | **Sustained fever** | Continuous bacteremia (unlike most bacterial infections) + endotoxin-mediated pyrogenic cytokine release (IL-1, TNF-α) | | **Hepatosplenomegaly** | RES hyperplasia + direct bacterial seeding of liver and spleen; organisms survive intracellularly in macrophages | **High-Yield:** Enteric fever is unique among bacterial infections for producing *sustained* fever (not spiking) due to continuous low-grade bacteremia — this distinguishes it from acute bacterial infections with spiking fever. **Clinical Pearl:** Rose spots, when present, are highly specific for enteric fever but are absent in >95% of cases. Their absence does not exclude the diagnosis. [cite:Harrison 21e Ch 157]
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