Cholera

Cholera, severe infectious disease endemic in India and some other tropical countries and occasionally spreading to temperate climates. The symptoms of cholera are diarrhea and the loss of water and salts in the stool. In severe cholera, the patient develops violent diarrhea 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 percent in untreated cases, but falls to less than 1 percent with proper treatment. Worldwide in 1999 more than 254,000 people were diagnosed with cholera and there were over 9,100 cholera-related deaths reported.

The causative agent of cholera is the bacterium Vibrio cholerae, which was discovered in 1883 by the German physician 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.

Control of the disease is still a major medical problem worldwide. The World Health Organization (WHO) estimates that 78 percent of the population in less developed countries is without clean water and 85 percent without adequate fecal waste disposal. Epidemics of cholera occurred in 1953 in Calcutta (now Kolkata), India; between 1964 and 1967 in South Vietnam; among Bangladeshi refugees fleeing to India during the civil war of 1971; in Latin America in 1991, and in Democratic Republic of the Congo in 1994 where the epidemic deaths were estimated at 23,800 within one month.

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 the WHO. Most patients recover in three to six days. Antibiotics such as tetracyclines, ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole can shorten the duration of the disease.

A vaccine made from killed 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.