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Cholera is caused by a comma-shaped bacterium, Vibrio cholerae, which is ingested in contaminated water and food. The bacteria multiply enormously in the intestine, where epithelial cells allow fluid to leak into the intestine with intense diarrhoea as a result. Cholera is endemic in India and other parts of the third world.
	The bacterium discovered by Robert Koch in 1884, can be killed by antibiotics, but the disease is caused by a bacterial toxin, which irreversibly activates the G proteins of epithelial cells in the intestine. This results in an often life-threatening loss of water and salts. From Koch's discovery of the cholera bacterium in 1884 it took researchers about 100 years to expose the real cause of the disease - the effect of the bacterial toxin on G proteins
The cholera bacterium is shaped like a comma with a tail (above).

1. The bacterium produces a toxin (above) that is the cause of the cholera. The toxin molecule is composed of several parts, one of which (coloured blue) penetrates the cell membrane (yellow)	2. The toxin acts as an enzyme that changes the G protein so that it can no longer switch itself off.
	3. The activated G protein changes the function of epithelial cells in the intestine, with enormous loss of water as a result. Cholera affects the intestine (left) because this is the place which the toxin reaches.
	4. Intestina villi (left), the minute projections from the mucous membrane of the small intestine, which are primarily affected by the toxin.