Cholera severe infectious disease endemic to India and some other tropical countries and occasionally spreading to temperate climates. The symptoms of cholera are diarrhoea and the loss of water and salts in the stool. In severe cholera, the patient develops violent diarrhoea with characteristic "rice-water stools", vomiting, thirst, muscle cramps, and, sometimes, circulatory collapse. Death can occur as quickly as a few hours after the onset of symptoms. The mortality rate is more than 50 per cent in untreated cases, but falls to less than 1 per cent with effective treatment.

The causative agent of cholera is the bacterium Vibrio cholerae, which was discovered in 1883 by the German doctor and bacteriologist Robert Koch. Virtually the only means by which a person can be infected is from food or water contaminated by bacteria from the stools of cholera patients. Prevention of the disease is therefore a matter of sanitation. Cholera epidemics swept through Europe and the United States in the 19th century but did not recur in those areas after improvement of the water supply. The connection between the disease and infected water sources was discovered by a London anaesthetist, Dr John Snow, during an epidemic that occurred in London in the 1850s, when he established that the source of infection came from contaminated water in a water pump in Broad Street.