Question
Pathogenesis of cholera
Answer
Pathogenesis of cholera (Vibrio cholerae):
V. cholerae is non-invasive; it colonizes the small intestinal mucosa via flagellar motility and adhesins, without penetrating the epithelium. The organism elaborates cholera toxin (choleragen), an AB-type exotoxin — the B subunit binds the GM1 ganglioside receptor on enterocytes, facilitating entry of the A subunit, which ADP-ribosylates the Gs protein, causing persistent activation of adenylate cyclase and a sustained rise in intracellular cAMP. This drives massive, unregulated active secretion of chloride (and passive water/sodium/bicarbonate) into the gut lumen, overwhelming the intestine’s absorptive capacity and producing the profuse, isotonic, rice-water diarrhoea characteristic of the disease, rapidly leading to severe dehydration and hypovolaemic shock if untreated. Notably, the mucosa itself remains structurally intact — the disease is purely a secretory/functional derangement, not a destructive/invasive process.