Cholera

Cholera is a gastrointestinal disease caused by Vibrio cholerae, which spreads through the consumption of contaminated water or food.

In the small intestine, the bacterium adheres to the epithelial cells.

The bacterium then releases cholera toxin, composed of one A subunit and five B subunits.

The B subunits bind to GM1 ganglioside receptors on the epithelial cell, allowing the toxin to enter the host cell by endocytosis.

Inside the cell, the A subunit is cleaved into A1 and A2 fragments.

The A1 fragment uses nicotinamide adenine dinucleotide as a donor to ADP-ribosylate the Gs protein, locking it in an active state.

As a result, adenylate cyclase becomes overstimulated and continuously converts ATP into cyclic AMP.

Elevated cyclic AMP levels open ion channels, causing anions like chloride and bicarbonate ions to rush into the intestinal lumen.

An osmotic gradient is created that draws water out of the cells.

The outcome is profuse watery diarrhea, which causes dehydration and electrolyte imbalance.