Cholera
Cholera is a serious infection of the intestine caused by the gram-negative bacterium Vibrio cholerae that produces severe diarrhea.
Several species of Vibrio bacteria cause diarrhea (see Section 9, Chapter 122), but the type that produces the most serious illness is Vibrio cholerae, the bacterium that causes cholera. Cholera may occur in large outbreaks of diarrheal illness. The disease is fatal in one third to one half of the people who do not receive proper medical care. Once common throughout the world, cholera is now largely confined to developing countries in the tropics and subtropics.
Vibrio cholerae normally lives in aquatic environments, attached to particular types of algae and plankton. People acquire the infection by ingesting water, seafood, or other foods contaminated with the bacteria. Once infected, people return the bacteria to the environment in their stool (particularly in regions where human waste is untreated), allowing explosive spread of the infection. The most recent cholera outbreak is still ongoing in Africa, where more than 400,000 people contracted the disease from 1998 to 1999.
Vibrio cholerae produces a toxin that causes the small intestine to secrete enormous amounts of fluid (in the form of watery diarrhea) that is rich in salts and minerals. It is the loss of fluid and minerals that causes death. The bacteria remain within the small intestine and do not invade tissues. Because the bacteria are sensitive to stomach acid, people with lower amounts of acid (such as young children and older people) are more susceptible to the disease. People living in areas where cholera is common (endemic) gradually acquire some immunity.
Symptoms and Diagnosis
Symptoms begin 1 to 3 days after infection and range from mild, uncomplicated diarrhea to severe, potentially fatal disease. Some infected people have no symptoms.
The disease starts with sudden, painless, watery diarrhea and vomiting. The amount of fluid lost through diarrhea and vomiting is proportional to the severity of the infection. In severe infections, the diarrhea causes a loss of more than 1 quart per hour. Within hours, the resulting depletion of fluid and salts leads to severe dehydration, with intense thirst, muscle cramps, weakness, and minimal urine production. Severe loss of fluid from tissues causes the eyes to become sunken and the skin on the fingers to become severely wrinkled. If the dehydration is not treated, the loss of fluid and salts can lead to kidney failure, shock, coma, and death.
Symptoms usually subside in 3 to 6 days. Most people are free of the bacteria in 2 weeks, but a few become long-term carriers.
A doctor confirms a diagnosis of cholera by recovering the bacteria from rectal swabs or from fresh stool samples.
Prevention and Treatment
Purification of water supplies and proper disposal of human waste are essential for controlling cholera. Other precautions include using boiled water and avoiding uncooked vegetables or inadequately cooked fish or shellfish. Shellfish tend to carry other forms of Vibrio as well.
Several vaccines for cholera are available outside the United States. These vaccines provide only partial protection and only for a limited time, and therefore are not generally recommended; new vaccines are currently being tested. Prompt treatment with the antibiotic tetracycline may help prevent the disease in household contacts of a person infected with cholera.
Rapid replacement of lost body fluids and salts is lifesaving, because people die from dehydration, not bacterial invasion. Most people with cholera can be treated effectively with fluids and salts given by mouth. Premixed packets of salts are available for use in areas prone to cholera epidemics, allowing people to make their own rehydration solution for home treatment when health care facilities are overwhelmed. The solution contains 20 grams of glucose, 3.5 grams of sodium chloride, 2.9 grams of sodium citrate, and 1.5 grams of potassium chloride per liter of boiled water. For severely dehydrated people who cannot drink, a salt solution is given intravenously. In epidemics, people sometimes receive fluids through a tube inserted through the nose into the stomach, because sufficient supplies for intravenous therapy are not available. Once dehydration is corrected, the goal of treatment is replacement of the exact amount of fluid lost through diarrhea and vomiting. Solid foods can be eaten after vomiting stops and appetite returns.
Early treatment with tetracycline or another antibiotic kills the bacteria and usually stops the diarrhea in 48 hours.
More than 50% of untreated people with severe cholera die. Less than 1% of people who receive prompt, adequate fluid replacement die.
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