Cholera :



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.
Control of the disease is still a major medical problem in several Asian countries. The World Health Organization (WHO) estimates that 78 per cent of the population in developing countries is without clean water and 85 per cent without adequate faecal waste disposal. Epidemics of cholera occurred in 1953 in Calcutta, India; between 1964 and 1967 in South Vietnam; among Bangladeshi refugees fleeing to India during the civil war of 1971; and in Peru in 1991. The 1971 outbreak killed about 6,500 people.
Treatment consists mainly of intravenous or oral replacement of fluids and salts. Packets for dilution containing the correct mixture of sodium, potassium, chloride, bicarbonate, and glucose have been made widely available by WHO. Most patients recover in three to six days. Antibiotics such as tetracyclines, ampicillin, chloramphenicol, and trimethoprim-sulphamethoxazole can shorten the duration of the disease.
A vaccine made from dead bacteria is commercially available and offers partial protection for a period of three to six months after immunization. Experimental studies have shown that the cholera bacterium produces a toxin that causes the small intestine to secrete large amounts of fluid, which leads to the fluid loss characteristic of the disease. This has led to work on a vaccine containing inactivated toxin. Attempts are also being made to develop a vaccine containing live bacteria that have been altered so that they do not produce the toxin.