Cholera is a serious, acute, infectious disease characterized by watery diarrhea that is caused by the bacterium Vibrio cholerae, first identified by Robert Koch in 1883 during a cholera outbreak in Egypt. The name of the disease comes from a Greek word meaning "flow of bile."
A false color transmission electron micrograph (TEM) of Vibrio cholerae bacterium magnified 6,000 times its original size.
Although cholera was a public health problem in the United States and Europe a hundred years ago, modern sanitation and the treatment of drinking water have virtually eliminated the disease in developed countries. In 2005, the World Health Organization (WHO) reported that there were 12 cases of cholera in the United States. Of these, eight were brought in by travelers and four were attributed to improperly cooked seafood in Louisiana following hurricanes Katrina and Rita.
Internationally, cholera outbreaks continue to occur in less developed countries, particularly following such natural disasters such as hurricanes and tsunamis during which water supplies become contaminated. In 2007, WHO reported that cholera occurred in 53 countries. A total of 177,693 cases and 4,031 cholera deaths were reported that year. However, WHO estimates that the number of reported cases represents only five to 10 percent of actual cases. In areas where cholera occurs, it is the most feared epidemic diarrheal disease because people can die from dehydration that results from severe diarrhea within hours of infection.
Cholera often occurs in major outbreaks or epidemics; seven pandemics (countrywide or worldwide epidemics) of cholera were recorded between 1817 and 2010. WHO estimates that during any cholera epidemic, approximately 0.2-1% of the local population will contract the disease.
Anyone can get cholera, but infants, children, pregnant women, and the elderly are more likely to die from the disease because they become dehydrated faster than adults. There is no particular season in which cholera is more likely to occur.
Cholera is spread by eating food or drinking water that has been contaminated with V. cholerae. Contamination usually occurs when human feces from a person who has the disease seeps into a community water supply. Fruits and vegetables also can be contaminated in areas where crops are fertilized with human feces. Cholera bacteria live in warm, brackish water and can infect persons who eat raw or undercooked seafood obtained from such waters. Cholera is rarely transmitted directly from one person to another.
Because of an extensive system of sewage and water treatment in the United States, Canada, Europe, Japan, and Australia, cholera is not a concern for visitors and residents of these countries. However, people visiting or living in other parts of the world, particularly the Indian subcontinent and in parts of Africa and South America, should be aware of the potential for contracting cholera and practice prevention. Fortunately, the disease is both preventable and treatable. Deaths usually occur in developing countries because of lack of access to hospitals and treatment.
Cholera is caused by the bacterium V. cholerae. This bacterium is a gram-negative aerobic bacillus, or rod-shaped bacterium. It has two major biotypes: classic and El Tor. El Tor is the biotype responsible for most of the cholera outbreaks reported from 1961 through the 2000s.
Because V. cholerae is sensitive to acid, most cholera-causing bacteria die in the acidic environment of the stomach. However, when a person has ingested food or water containing large amounts of cholera bacteria, some will survive to infect the intestines. As would be expected, antacid usage or the use of any medication that blocks or reduces acid production in the stomach allows more bacteria to survive and cause infection.
In the small intestine, the rapidly multiplying bacteria produce a toxin that causes a large volume of water and electrolytes to be secreted into the bowels and then to be abruptly eliminated in the form of watery diarrhea. Vomiting may also occur. Symptoms begin to appear between one and three days after contaminated food or water has been ingested.
Most cases of cholera are mild, but about one in 20 patients experience severe, potentially life-threatening symptoms. In severe cases, fluids can be lost through diarrhea and vomiting at the rate of one quart per hour. This loss of fluid can produce a dangerous state of dehydration unless the lost fluids and electrolytes are rapidly replaced.
Signs of dehydration include intense thirst, little or no urine output, dry skin and mouth, an absence of tears, glassy or sunken eyes, muscle cramps, weakness, and rapid heart rate. The fontanelle (soft spot on an infant's head) will appear to be sunken or drawn in. Dehydration occurs most rapidly in the very young and the very old because they have fewer fluid reserves. A doctor should be consulted immediately any time signs of severe dehydration occur. Immediate replacement of lost fluids and electrolytes is necessary to prevent kidney failure, coma, and death.
Some people are at greater risk of having a severe case of cholera if they become infected. These risk factors include:
Rapid diagnosis of cholera can be made by examining a fresh stool sample under the microscope for the presence of V. cholerae bacteria. Cholera can also be diagnosed by culturing a stool sample in the laboratory to isolate the cholera-causing bacteria. In addition, a blood test may reveal the presence of antibodies against the cholera bacteria. Because of the speed at which life-threatening dehydration can occur, in areas where cholera occurs often, however, patients are usually treated for diarrhea and vomiting symptoms as if they had cholera without laboratory confirmation.
The key to treating cholera lies in preventing dehydration by replacing fluids and electrolytes lost through diarrhea and vomiting. The discovery that rehydration can be accomplished orally revolutionized the treatment of cholera and other, similar diseases by making this simple, cost-effective treatment widely available throughout the world. WHO has developed an inexpensive oral replacement fluid containing appropriate amounts of water, sugar, and salts that is used worldwide. In cases of severe dehydration, replacement fluids must be given intravenously. Patients should be encouraged to drink when they can keep liquids down and eat when their appetite returns. Recovery generally takes three to six days.
Adults may be given the antibiotic tetracycline to shorten the duration of the illness and reduce fluid loss. WHO recommends this antibiotic treatment only in cases of severe dehydration. If antibiotics are overused, the cholera bacteria may develop resistance to the drug, making the antibiotic ineffective in treating even severe cases of cholera. Tetracycline is not given to children whose permanent teeth have not come in because it can cause the teeth to become permanently discolored.
A possible complementary or alternative treatment for fluid loss caused by cholera is a plant-derived compound, an extract made from the tree bark of Croton lechleri, the Sangre de grado tree found in the South American rain forest. Researchers at a hospital research institute in California report that the extract appears to work by preventing the loss of chloride and other electrolytes from the body.
Cholera is a very treatable disease so long as resources are available for rehydration. Patients with milder cases of cholera usually recover on their own in three to six days without additional complications. Theymay eliminate the bacteria in their feces for up to two weeks. Chronic carriers of the disease are rare. With prompt fluid and electrolyte replacement, the death rate in patients with severe cholera is less than one percent. Untreated, the death rate can be greater than 50%. The difficulty in treating severe cholera does not lie in not knowing how to treat it but rather in getting medical care to the sick in developing areas of the world where medical resources are limited.
The best form of cholera prevention is to establish good sanitation and waste treatment systems. In the absence of adequate sewage treatment, the following guidelines should be followed to reduce the possibility of infection:
Preventive measures following natural disasters include guaranteeing the purity of community drinking water, either by large-scale chlorination and boiling, or by bringing in bottled or purified water from the outside. Other important preventive measures at the community level include provision for the safe disposal of human feces and good food hygiene.
Because cholera is one of the few infectious diseases that can be spread by human remains (through fecal matter leaking from corpses into the water supply), during natural disasters, emergency workers who handle human remains are at increased risk of infection. It is considered preferable to bury corpses rather than to cremate them, however, and to allow survivors time to conduct appropriate burial ceremonies or rituals. The remains should be disinfected prior to burial, and buried at least 90 feet (30 m) away from sources of drinking water.
A cholera vaccines exists that can be given to travelers and residents of areas where cholera is known to be active, but the vaccine is not highly effective. It provides only 25-50% immunity, and then only for a period of about six months. The vaccine is never given to infants under six months of age. The Centers for Disease Control and Prevention (CDC) does not currently recommend cholera vaccination for travelers. Residents of cholera-plagued areas should discuss the value of the vaccine with their doctor.
In 2006 another cholera vaccine known as WC/rBS was approved for use in the United States. It is also available in Sweden. This vaccine is designed to stimulate the formation of antibodies against both the cholera bacteria and the cholera toxin. It is more effective than previous vaccines but provides protection for only a limited time. The prevention strategies listed previously are still necessary precautions.