## Pathogenesis of Rotavirus-Induced Diarrhea ### Primary Mechanism **Key Point:** Rotavirus causes diarrhea primarily through **direct cytopathic destruction of villous epithelial cells** in the small intestine, leading to **malabsorption** and **osmotic diarrhea**. ### Pathophysiological Sequence ```mermaid flowchart TD A[Rotavirus ingestion]:::outcome --> B[Replication in villous epithelial cells]:::action B --> C[Villous atrophy and epithelial cell destruction]:::action C --> D{Intestinal dysfunction}:::decision D -->|Reduced absorptive surface| E[Malabsorption of water and electrolytes]:::outcome D -->|Osmotic effect of unabsorbed sugars| F[Osmotic diarrhea]:::outcome E --> G[Acute watery diarrhea]:::outcome F --> G ``` ### Cellular Pathology **High-Yield:** Rotavirus infection causes: - **Villous blunting and shortening** (reduced absorptive surface area) - **Epithelial cell necrosis and desquamation** - **Crypt hyperplasia** (compensatory response) - **Reduced disaccharidase activity** (especially lactase), worsening malabsorption ### Non-Secretory Nature **Clinical Pearl:** Unlike cholera or enterotoxigenic *E. coli* (ETEC), rotavirus diarrhea is **non-secretory**. There is no toxin-mediated activation of cAMP or guanylate cyclase. The diarrhea is due to **structural damage and reduced absorption**, not increased secretion. ### Stool Characteristics - **Osmolarity:** High (osmotic diarrhea) - **Stool osmotic gap:** >100 mOsm/kg (indicates malabsorption) - **pH:** Acidic (due to bacterial fermentation of unabsorbed carbohydrates) **Mnemonic:** **ROTA** = **R**eduction **O**f **T**ransport **A**bility (malabsorption-driven diarrhea). [cite:Robbins and Cotran Pathologic Basis of Disease 10e Ch 17]
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