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.
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
in several Asian countries. 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; and in Peru in 1991. The 1971 outbreak
killed about 6500 persons. 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.