Cholera

Introduction

Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues

Primary Source Connection

BIBLIOGRAPHY

Introduction

Cholera, sometimes called Asiatic cholera or epidemic cholera, is a disease with roots in antiquity that remains a global threat. Many parts of the world have been hit by major epidemics over the course of human history. Cholera is an acute intestinal infection caused by the bacterium Vibrio cholerae. It can cause very rapid dehydration of the body, which can be fatal. Cholera is transmitted by contaminated food and water. It is endemic—that is, present all the time—in countries where there is inadequate access to clean water. Treatment of cholera is simple and relies on restoring the fluids lost by the body. However, even this simple treatment may not be available in very poor countries. The best approach to preventing cholera lies in better sanitation—improving public health through adequate sewage disposal and cleaning up the water supply. In many less developed countries, this is a difficult challenge to meet, since it requires political stability and increased investment in the national infrastructure.

Disease History, Characteristics, and Transmission

V. cholerae belongs to the Vibrio genus of Gram-negative bacteria. The term Gram-negative refers to the way in which a bacterium absorbs visualizing stains under a microscope for identification purposes. Vibrio species exist as straight or curved rods in watery environments. These bacteria use a whiplike projection called a flagellum to propel themselves. (The flagellum is an extension to the bacterial cell body.) Vibrio species prefer marine environments and grow best in the presence of salt. They are one of the most common organisms in the surface waters of the world.

There are 139 serotypes of V. cholerae—they are basically all the same species, but are distinguished by the number and type of antigen (protein) molecules on their cell surfaces. Most cholera infections are caused by the V. cholerae 01 serotype, but others have been found in specific outbreaks or epidemics. For instance, the El Tor serotype was first isolated in the quarantine station of the same name in Sinai in 1906, and was linked to an outbreak among pilgrims returning from Mecca. It seems to survive for longer than the 01 serotype, which is killed by 15 minutes of heating. In 1992, the 0139 serotype was first identified in Madras and was responsible for outbreaks in Bangladesh and Thailand during the following year.

Most people infected with V. cholerae do not actually become ill, although the bacterium is present in their feces for seven to 14 days, which means they may contaminate food or water. However, V. cholerae 01 and a few other serotypes produce a potent toxin that affects the mucosal lining of the small intestine, causing severe diarrhea, with very rapid onset. The incubation period of V. cholerae ranges from just a few hours to five days. In most cases, the illness is difficult to distinguish from other diarrheal diseases. But, in severe cholera, the diarrhea is copious—the patient may lose more than a quart (liter) of fluid every hour. Microscopic examination of stool samples reveals the presence of V. cholerae as “shooting stars”—as the bacteria use their flagella to dart through the sample. Pathologists may call a sample “rice-water stool” due to its appearance—clear, but flecked with mucus and cells. The diarrhea may be accompanied by vomiting, but pain and fever are minimal and certainly out of proportion to the severity of the diarrhea.

Severe cholera can lead to dehydration, through a combination of diarrhea and vomiting. The patient may enter a state of shock due to massive fluid loss and electrolyte imbalance, suffering seizures, kidney failure, heart rhythm abnormalities, and unconsciousness. Death from dehydration and shock may occur within hours. As a result, cholera is always considered a medical emergency and, indeed, it is one of the most rapidly fatal illnesses ever known. Left untreated, severe cholera has a death rate of 30–50%, but when treated promptly, mortality falls to less than 1%.

Transmission of V. cholerae is through the fecal-oral route, which, in practical terms, means the consumption of, or contact with, contaminated food and water. V. cholerae is hard to avoid in places where sanitation is poor and access to clean water for drinking or washing is limited or non-existent. Imported foodstuffs are only a rare cause of cholera, and the risk can be kept at bay through high standards of food handling hygiene.

Scope and Distribution

Cholera affects many countries around the world. According to the latest data from the World Health Organization (WHO), there were 131,943 cases reported in 2005, including 2,272 deaths, from 52 countries. This represents a 30% increase over 2004, although the number of countries reporting cholera was down from 56. The 2005 increase can be largely accounted for by a series of outbreaks in 14 countries in West Africa, including Senegal, Guinea-Bissau, Ghana, Guinea, and Mauritania. The latter, and Gambia, had previously been free from cholera for over a decade, so this is a downturn for them. Indeed, Africa accounted for about 95% of all cholera cases, although the number of cases from Asia also increased by 18%. The Indian subcontinent accounted for nearly half of all the Asian cases. There were 12 cases in the United States—four of them related to Hurricane Katrina—and ten in Europe. Globally, WHO admits that the toll from cholera is much higher, because surveillance and reporting systems are far from perfect. Some countries only report laboratory-confirmed cases, and there is often confusion over what is and is not cholera.

Cholera is rare in areas where basic hygiene standards can be assured. However, there has been a source of cholera present in the Gulf of Mexico since at least 1973. This has led to sporadic cholera cases in Texas, Louisiana, Georgia, and Florida, linked to eating crabs, shrimp, or oysters that were not properly cooked or stored.

Treatment and Prevention

The most important treatment for cholera is fluid and electrolyte (salt) replacement to treat the losses caused by diarrhea and vomiting. Oral rehydration fluid, containing glucose and salt dissolved in water, is the most convenient form of this treatment. Eighty percent of all cases of cholera can be treated in this way, and the treatment needs to be continued until the diarrhea stops. Intravenous administration of rehydration fluid sometimes may be necessary. In countries where oral rehydration fluid is not available, water in which rice has been boiled provides a good alternative. Where antibiotic treatment is needed, tetracycline is the drug of choice and has been shown to shorten the duration of the disease. Ampicillin is a suitable alternative for children and pregnant women.

Clean water and effective sanitation are the most effective preventive measures against cholera. Chlorination of water, boiling of water in households, and the construction and maintenance of latrines are basic measures that can help achieve these goals. High standards of personal hygiene and food preparation can also reduce the spread of the disease. Accurate and ongoing surveillance of outbreaks and epidemics can help reduce the toll from cholera.

WORDS TO KNOW

ELECTROLYTES: Compounds that ionize in a solution; electrolytes dissolved in the blood play an important role in maintaining the proper functioning of the body.

FECAL-ORAL ROUTE: The transmission of minute particles of fecal material from one organism (human or animal) to the mouth of another organism.

There are now three oral vaccines against cholera, and research has shown them to be safe, effective, and capable of mounting an immune response against the disease. They are suitable for travelers, but WHO is also carrying out trials of mass vaccinations among vulnerable populations. Trials of one vaccine that have been carried out in Bangladesh and Peru show that it gives protection for at least six months among all age groups. A second cholera vaccine is being produced and tested in Vietnam, and there are plans to use this vaccine in India. The results on the third vaccine, not currently being produced, have been less convincing, although it has been shown to be safe.

Impacts and Issues

Cholera is one of the great killers of all time. The characteristic symptoms of the disease were described by the Greek physician Hippocrates (c.460–c.357 BC), and the disease is also mentioned by early Indian and Chinese writers. Epidemic cholera was first described in 1563 by Garcia del Huerto, a Portuguese physician working in Goa, India. The natural “home” of cholera appears to be the Ganges plain and delta in northern India and Bangladesh. From here, it spread along trade routes, although for many centuries the disease was generally confined to India. Beginning in the nineteenth century, cholera began to spread around the world as trade expanded. Between 1817 and 1923, there were six pandemics. It was the second pandemic, beginning in 1824, that brought cholera to England (1831), North America (1832), and the Caribbean and Latin America (1833).

The seventh pandemic of cholera, caused by the El Tor serotype, began in 1961 and affected the Far East, although most of Europe was spared. During the 1980s, outbreaks of cholera were common in refugee camps and city slums in famine and war-stricken countries such as Ethiopia and Sudan. The disease, carried by the El Tor serotype, returned to the Western Hemisphere in the early 1990s, beginning in Peru—where it had been absent for over 100 years—and spreading outwards through Latin America. In 1992, a large epidemic in Bangladesh was attributed to the newly identified 0139 serotype.

The rapid onset and high mortality of cholera brought great fear to populations during the nineteenth century, as it affected many areas for the first time. Many people thought the cause of cholera—and other diseases—was “miasma” or “bad air.” Therefore, the standard treatment was to burn huge bonfires to cleanse the air. However, some blamed cholera on low morals and drunkenness. The belief that “cleanliness is next to Godliness” at least led to the beginnings of an interest in public health in England and America. Social reformers began to campaign for piped water, drains, and proper sewage disposal. Although these changes took many years to bring about, they eventually made a significant contribution towards cutting the death toll from cholera and many other infectious diseases.

It was the English physician John Snow (1813– 1858) who suggested that contaminated water, rather than bad air, caused the transmission of cholera. He carried out a serious scientific investigation during the 1848 epidemic in London. His classic work on the subject is titled “On the Mode of Communication of Cholera.” In August 1854, there was a fresh outbreak of cholera in and around Broad Street, near Snow's own home. He suggested removing the handle from the Broad Street pump, since this was the probable source of the outbreak. This was done and thereafter there were no more major cholera outbreaks in London.

Snow also accepted the germ theory of disease, put forward by the Louis Pasteur (1822–1895) and Robert Koch (1843–1910). In 1882, Koch discovered the bacillus that causes tuberculosis—also a major killer—and the following year, working in Egypt, he identified V. cholerae as the cause of cholera.

Thanks to Snow, Koch, and other researchers, cholera is a well-understood disease in scientific and clinical terms. The causative agents have been discovered, an effective cure is known, and there are vaccines against the disease. Its continuing existence is not due to a lack of scientific understanding or effective treatment and prevention options but to the economic and political factors in many countries that affect their level of development. Today, WHO says that most developing countries face the threat of a cholera outbreak or epidemic. According to WHO and its Global Task Force on Cholera Control, improvements in sanitation and access to clean water represent the only sustainable approach to cholera prevention and control. These factors are more important than drugs to treat the disease or vaccines to protect against it. In areas of the world afflicted by poverty or war (or both), the high standards of public health that are taken for granted in the West are too often hard to achieve and sustain.

The response to cholera is too often reactive—that is, dealing with an outbreak or epidemic once it has occurred. Fighting the threat of cholera requires a multidisciplinary approach involving a country's agriculture, water, health, and education sectors. Investment in infrastructure, including construction of water and sewage treatment plants, is key to improving public health. Long-term planning is needed so that attention is given not just to responding to cholera when it happens— although that is important—but also to prevention and surveillance. There is a need for far more openness and transparency on surveillance and reporting. Some countries fear that reporting a cholera outbreak will lead to travel and trade restrictions that will hurt their economy.

Because the above goals may be difficult to achieve in many countries, especially in urban slums and in crisis situations, the use of oral cholera vaccines as a complementary management tool is becoming more popular. For example, in 2002–2003 a mass vaccination campaign— the first in an endemic setting—was carried out in Beira, Mozambique, where there are yearly outbreaks. Vaccinated people were shown to have a high level of protection from cholera. Other mass vaccinations have been carried out in emergency settings—in Darfur in Sudan in 2004, for example. These campaigns are challenging, since they are costly and hard to implement, but WHO regards the experience gained as encouraging.

Cholera often is a seasonal disease, occurring each year during the rainy season. For example, in Bangladesh, where it is endemic, cholera comes after the monsoons. This is related to an increase in the growth of algae during the rainy season in the watery environment inhabited by V. cholerae. The algae and the bacteria form a symbotic (mutually beneficial) relationship, which allows the bacteria to survive indefinitely in contaminated water. Cholera is also associated with floods and cyclones and often spreads in times of war, especially in refugee camps, because upheaval and overcrowding cause the breakdown of basic facilities, such as water supply. For example, about 45,000 people died of cholera in refugee camps during the war in Rwanda in 1994.

The Global Task Force on Cholera Control has been considering how to improve the use of vaccination as a control tool. It is looking for ways to identify the populations most at risk and protocols for proper use of vaccines in complex emergency settings. Many countries are making significant efforts to control the spread of cholera. For example, there was an outbreak of 1,133 cases in Iran in 2005, including 11 deaths, but this outbreak was rapidly brought under control because the government was able to mount an effective emergency response. However, there are also increasing numbers of vulnerable people living in unsanitary conditions. For instance, in Afghanistan there was a recent outbreak of more than 150,000 cases of an acute watery diarrhea that WHO considers to be cholera. In the future, global warming may lead to more frequent droughts, which have also been linked to cholera outbreaks.

BOIL IT, COOK IT, PEEL IT, OR FORGET IT

The Division of Bacterial and Mycotic Diseases at the Centers for Disease Control and Prevention (CDC) states that “when simple precautions are observed, contracting the disease (cholera) is unlikely” and offers the following recommendations for travelers to lower their risk of cholera.

All travelers to areas where cholera has occurred should observe the following recommendations:

• Drink only water that you have boiled or treated with chlorine or iodine. Other safe beverages include tea and coffee made with boiled water and carbonated, bottled beverages with no ice.
• Eat only foods that have been thoroughly cooked and are still hot, or fruit that you have peeled yourself.
• Avoid undercooked or raw fish or shellfish, including ceviche.
• Make sure all vegetables are cooked. Avoid salads.
• Avoid foods and beverages from street vendors.
• Do not bring perishable seafood back to the United States.

A simple rule of thumb is “Boil it, cook it, peel it, or forget it.”

SOURCE: Centers for Disease Control and Prevention (CDC)

Primary Source Connection

Sometimes the fear of disease can be as captivating as the reality. Although rare in industrialized nations for more than a century, cholera still raises a powerful and feared specter, especially following disasters that devastate local sanitation resources. The essay below reflects on the fear of widespread cholera following Hurricane Katrina's landfall in along the Mississippi Gulf Coast and the devastation of New Orleans by flooding after levee breaks. The author, Steven Shapin, is Franklin L. Ford Professor of the History of Science at Harvard University. Shapin previously served as Professor of Sociology at the University of California, San Diego, and at Edinburgh University. He is a frequent contributor to the The New Yorker magazine.

IN CONTEXT: ACCESS TO IMPROVED SANITATION

The list below reflects selected data from the World Health Organization (WHO) that demonstrates the wide disparity in results reported by WHO as of February 2007 for the relative percentage of the population of a country reported to have access to improved sanitation.

• Afghanistan 8% of the population (year reported: 2002)
• Chad 8% (2002)
• Congo 9% (2002)
• Eritrea 9% (2002)
• Niger 12% (2002)
• India 30% (2002)
• Nigeria 38% (2002)
• Uganda 41% (2002)
• Viet Nam 41% (2002)
• Rwanda 41% (2002)
• China 44% (2002)
• Romania 51% (2002)
• Guatemala 61% (2002)
• Mexico 77% (2002)
• Iraq 80% (2002)
• Iran (Islamic Republic of) 84% (2002)
• Russian Federation 87% (2002)
• Tonga 97% (2002)
• Cuba 98% (2002)
• Ukraine 99% (2002)
• Canada 100% (2002)
• United States of America 100% (2002)
• United Arab Emirates 100% (2002)

SOURCE: World Health Organization (WHO)

Sick City

After Katrina, cholera. On August 31, 2005—two days after the hurricane made landfall—the Bush Administration's Health and Human Services Secretary warned, “We are gravely concerned about the potential for cholera, typhoid, and dehydrating diseases that could come as a result of the stagnant water and other conditions.” Around the world, newspapers and other media evoked the spectre of cholera in the United States, the world's hygienic superpower. A newspaper in Columbus, Ohio, reported that New Orleans was a cesspool of “enough cholera germs to wipe out Los Angeles.” And a paper in Tennessee, where some New Orleans refugees had arrived, whipped up fear among the locals with the headline “KATRINA EVACUEE DIAGNOSED WITH CHOLERA.”

There was to be no outbreak of cholera in New Orleans, nor among the residents who fled. Despite raw sewage and decomposing bodies floating in the toxic brew that drowned the city, cholera was never likely to happen: there was little evidence that the specific bacteria that cause cholera were present. But the point had been made: Katrina had reduced a great American city to Third World conditions. Twenty-first-century America had had a cholera scare.

Cholera is a horrific illness. The onset of the disease is typically quick and spectacular; you can be healthy one moment and dead within hours. The disease, left untreated, has a fatality rate that can reach fifty per cent. The first sign that you have it is a sudden and explosive watery diarrhea, classically described as “rice-water stool,” resembling the water in which rice has been rinsed and sometimes having a fishy smell. White specks floating in the stool are bits of lining from the small intestine. As a result of water loss—vomiting often accompanies diarrhea, and as much as a litre of water may be lost per hour—your eyes become sunken; your body is racked with agonizing cramps; the skin becomes leathery; lips and face turn blue; blood pressure drops; heartbeat becomes irregular; the amount of oxygen reaching your cells diminishes. Once you enter hypovolemic shock, death can follow within minutes. A mid-nineteenth-century English newspaper report described cholera victims who were “one minute warm, palpitating, human organisms—the next a sort of galvanized corpse, with icy breath, stopped pulse, and blood congealed—blue, shrivelled up, convulsed.” Through it all, and until the very last stages, is the added horror of full consciousness. You are aware of what's happening: “the mind within remains untouched and clear,—shining strangely through the glazed eyes … a spirit, looking out in terror from a corpse.”

You may know precisely what is going to happen to you because cholera is an epidemic disease, and unless you are fortunate enough to be the first victim you have probably seen many others die of it, possibly members of your own family, since the disease often affects households en bloc. Once cholera begins, it can spread with terrifying speed. Residents of cities in its path used to track cholera's approach in the daily papers, panic growing as nearby cities were struck. Those who have the means to flee do, and the refugees cause panic in the places to which they've fled. Writing from Paris during the 1831–32 epidemic, the poet Heinrich Heine said that it “was as if the end of the world had come.” The people fell on the victims “like beasts, like maniacs.”

Cholera is now remarkably easy to treat: the key is to quickly provide victims with large amounts of fluids and electrolytes. That simple regime can reduce the fatality rate to less than one per cent. In 2004, there were only five cases of cholera reported to the Centers for Disease Control, four of which were acquired outside the U.S., and none of which proved fatal. Epidemic cholera is now almost exclusively a Third World illness—often appearing in the wake of civil wars and natural disasters—and it is a major killer only in places lacking the infrastructure for effective emergency treatment. Within the last several years, there has been cholera in Angola, Sudan (including Darfur), the Democratic Republic of the Congo, and an arc of West African countries from Senegal to Niger. In the early nineteen-nineties, there were more than a million cases in Latin America, mass deaths from cholera among the refugees from Rwandan genocide in 1994, and regular outbreaks in India and Bangladesh, especially after floods. The World Health Organization calls cholera “one of the key indicators of social development.” Its presence is a sure sign that people are not living with civilized amenities.

Of course, this is a state that continues to elude much of the world—including all those underdeveloped countries which are currently experiencing what epidemiologists call the Seventh Pandemic. The problem is no longer an incorrect understanding of the cause: around the world, people have known for more than a century what you have to do to prevent cholera. Rather, cholera persists because of infrastructural inadequacies that arise from such social and political circumstances as the Third World's foreign-debt burdens, inequitable world-trade regimes, local failures of urban planning, corruption, crime, and incompetence. Victorian London illustrates how much could be done with bad science; the continuing existence of cholera in the Third World shows that even good science is impotent without the resources, the institutions, and the will to act.

Steven Shapin

SHAPIN, STEVEN. “SICK CITY.” THE NEW YORKER (NOV 6, 2006).

See AlsoPublic Health and Infectious Disease; Sanitation; War and Infectious Disease; Water-borne Disease.

BIBLIOGRAPHY

Books

Gates, Robert H. Infectious Disease Secrets. 2nd ed. Philadelphia: Hanley and Beltus, 2003.

Lock, Stephen, John M. Last, and George Dunea. The Oxford Illustrated Companion to Medicine. Oxford: Oxford University Press, 2001.

Porter Roy, ed. Cambridge Illustrated History of Medicine. Cambridge: Cambridge University Press, 1996.

Wilson, Walter R., and Merle A. Sande. Current Diagnosis & Treatment in Infectious Diseases. New York: McGraw Hill, 2001.

Periodicals

“Cholera 2005.” World Health Organization Weekly Epidemiological Record 81 (August 4, 2006): 297–308. This article can be found online at <http://www.who.int/wer/2006/wer8131/en/index.html>.

Web Sites

Centers for Disease Control and Prevention. “Cholera.”

October 6, 2005. <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/cholera_g.htm> (accessed February 13, 2007).

University of California, Los Angeles. School of Public Health. Department of Epidemiology. “John Snow.” <http://www.ph.ucla.edu/epi/snow.html> (accessed February 13, 2007).

World Health Organization. “Cholera.” <http://www.who.int/topics/cholera/en/> (accessed February 13, 2007).

Susan Aldridge

Cholera

Definition

Cholera is an 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."

Cholera is spread by eating food or drinking water contaminated with the bacterium. 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. Cholera outbreaks, however, still occur from time to time in less developed countries, particularly following such natural disasters as the tsunami that struck countries surrounding the Indian Ocean in December 2004. In these areas cholera is still the most feared epidemic diarrheal disease because people can die within hours of infection from dehydration due to the loss of water from the body through the bowels.

V. cholerae 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 early 2000s.

Description

Cholera is spread by eating food or drinking water that has been contaminated with cholera bacteria. Contamination usually occurs when human feces from a person who has the disease seeps into a community water supply. Fruits and vegetables can also be contaminated in areas where crops are fertilized with human feces. Cholera bacteria also 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.

Cholera often occurs in outbreaks or epidemics; seven pandemics (countrywide or worldwide epidemics) of cholera have been recorded between 1817 and 2003. The World Health Organization (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, 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.

Because of an extensive system of sewage and water treatment in the United States, Canada, Europe, Japan, and Australia, cholera is generally not a concern for visitors and residents of these countries. Between 1995 and 2000, 61 cases of cholera in American citizens were reported to the Centers for Disease Control and Prevention (CDC); only 24 represented infections acquired in the United States. People visiting or living in other parts of the world, particularly on 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.

Causes and symptoms

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 acid production in the stomach would allow 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 the 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 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 the 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:

• People taking proton pump inhibitors, histamine blockers, or antacids to control acid indigestion. As noted earlier, V. cholerae is sensitive to stomach acid.
• People who have had chronic gastritis caused by infection with Helicobacter pylori.
• People who have had a partial gastrectomy (surgical removal of a portion of the stomach).

Diagnosis

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. In areas where cholera occurs often, however, patients are usually treated for diarrhea and vomiting symptoms as if they had cholera without laboratory confirmation.

Treatment

The key to treating cholera lies in preventing dehydration by replacing the 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. The World Health Organization 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. The World Health Organization recommends this antibiotic treatment only in cases of severe dehydration. If antibiotics are overused, the cholera bacteria organism may become resistant 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.

Other antibiotics that may be given to speed up the clearance of V. cholerae from the body include ciprofloxacin and erythromycin.

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.

Prognosis

Today, cholera is a very treatable disease. Patients with milder cases of cholera usually recover on their own in three to six days without additional complications. They may 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 1%. 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 underdeveloped areas of the world where medical resources are limited.

Prevention

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:

• Boil it. Drink and brush teeth only with water that has been boiled or treated with chlorine or iodine tablets. Safe drinks include coffee and tea made with boiling water or carbonated bottled water and carbonated soft drinks.
• Cook it. Eat only thoroughly cooked foods, and eat them while they are still hot. Avoid eating food from street vendors.
• Peel it. Eat only fruit or nuts with a thick intact skin or shell that is removed immediately before eating.
• Forget it. Do not eat raw foods such as oysters or ceviche. Avoid salads and raw vegetables. Do not use untreated ice cubes in otherwise safe drinks.
• Stay out of it. Do not swim or fish in polluted water.

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), 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 vaccine 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 do not currently recommend cholera vaccination for travelers. Residents of cholera-plagued areas should discuss the value of the vaccine with their doctor.

A newer cholera vaccine known as Peru-15 underwent phase II trials in the summer of 2003. As of mid-2004, the manufacturer is planning phase III trials in a developing country and in travelers. Peru-15 is classified as a single-dose recombinant vaccine.

Resources

BOOKS

Beers, Mark H., MD, and Robert Berkow, MD, editors. "Bacterial Diseases." Section 13, Chapter 157. In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2002.

PERIODICALS

Altman, Lawrence K., MD, and Denise Grady. "Water Is Key to Averting Epidemics Along Coasts." New York Times December 30, 2004.

Fischer, H., T. E. Machen, J. H. Widdicombe, et al. "A Novel Extract SB-300 from the Stem Bark Latex of Croton lechleri Inhibits CFTR-Mediated Chloride Secretion in Human Colonic Epithelial Cells." Journal of Ethnopharmacology 93 (August 2004): 351-357.

Handa, Sajeev. "Cholera." eMedicine. [cited March 21, 2003]. 〈http://www.emedicine.com/med/topic351.htm〉.

Jones, T. "Peru-15 (AVANT)." Current Opinion in Investigational Drugs 5 (August 2004): 887-891.

ORGANIZATIONS

Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. 〈http://www.cdc.gov〉.

Infectious Diseases Society of America (IDSA). 66 Canal Center Plaza, Suite 600, Alexandria, VA 22314. (703) 299-0200. Fax: (703) 299-0204. 〈http://www.idsociety.org〉.

World Health Organization (WHO). 〈http://www.who.int/en/〉.

OTHER

World Health Organization Fact Sheet. "Cholera." Fact sheet No. 107, March 2000. 〈http://www.who.int/mediacentre/factsheets/fs107/en/〉.

World Health Organization Fact Sheet. "Flooding and Communicable Diseases Fact Sheet: Risk Assessment and Preventive Measures." December 2004. 〈http://www.who.int/hac/techguidance/ems/flood_cds/en/index.html〉.

KEY TERMS

Antibody— A specific protein produced by the immune system in response to a specific foreign protein or particle called an antigen.

Bacillus— A rod-shaped bacterium. The organism that causes cholera is a gram-negative bacillus.

Biotype— A variant strain of a bacterial species with distinctive physiological characteristics.

Electrolytes— Salts and minerals that ionize in body fluids. Common human electrolytes are sodium, chloride, potassium, and calcium. Electrolytes control the fluid balance of the body and are important in muscle contraction, energy generation, and almost all major biochemical reactions in the body.

Pandemic— A widespread epidemic that affects whole countries or the entire world. There have been seven cholera pandemics since 1817.

Toxin— A poison. In the case of cholera, a poison secreted as a byproduct of the growth of the cholera bacteria in the small intestine.

Cholera

The cause of cholera

Transmission of cholera

Symptoms and treatment of cholera

Resources

Cholera is among the most devastating of all human diseases. Although endemic in some areas of the world, cholera is usually associated with massive migrations of people, such as those occurring during war or famine. Cholera is also common in developing countries, where suboptimal sanitation practices are responsible for its spread. If not treated, cholera has a fatality rate of over 60%. Death results from dehydration, a consequence of the severe diarrhea and vomiting that characterize this disease. In the last 15 years, treatment strategies have been devised that have cut the fatality rate of cholera to 1%. Preventive measures have also reduced the incidence of cholera outbreaks. These measures, however, require swift intervention, which is not always possible during the social upheavals that can lead to cholera epidemics.

The cause of cholera

Cholera is caused by a bacteria called Vibrio cholerae, which secretes a toxin, or poison, that binds to the cells of the small intestine. One of the functions of the small intestine in humans is to regulate the amount of fluid that is absorbed by cells. Normally, small intestine cells absorb most of the fluid that is ingested; only a small amount of fluid is excreted in the feces. Under abnormal conditions, such as in response to a pathogen, cells do not absorb fluid, and as a result a lot of fluid enters the small intestine and is excreted in the feces. These frequent, watery stools are called diarrhea. Diarrhea can actually be helpful, as the rapid movement of fluid flushes the gastrointestinal tract of harmful bacteria and other pathogens, but if diarrhea is severe or long lasting, such as occurs in cholera, too much fluid is lost and the body becomes dehydrated. If fluids are not replaced, death can result.

Along with causing fluid loss, the binding of cholera toxin to small intestine cells also results in loss of electrolytes. Electrolytes are chemicals that the body needs to function properly, such as potassium chloride, sodium chloride (salt), and bicarbonate. Electrolytes are crucial in the control of blood pressure, excretion of metabolic wastes, and maintenance of blood sugar levels. If the amount of electrolytes in the body deviates even slightly, these crucial body functions are imperiled. Cholera toxin prompts the small intestine cells to secrete large amounts of electrolytes into the small intestine. These electrolytes are then excreted in the watery diarrhea.

The cholera toxin consists of two subunits, the A subunit and the B subunit. The B subunit is a ring, and the A subunit is suspended within it. By itself, the B subunit is nontoxic; the A subunit is the poisonous part of the toxin. The B subunit binds to the small intestine cell and creates a channel within the cell membrane through which the A subunit enters. Once inside the small intestine cell, the A subunit disrupts the cascade of reactions that regulates the cell’s fluid and electrolyte balance. Fluid and electrolytes leave the cell and enter the small intestine. The resultant diarrhea may cause a fluid loss that exceeds 1 qt (1 l) per hour.

V. cholerae lives in aquatic environments and especially favors salty or brackish waters. V. cholerae frequently colonize shellfish; in fact, cholera cases in the United States are almost always traced to eating raw or undercooked shellfish. Interestingly, V. cholerae can also cause skin and other soft tissue infections. Cases of such infection with these bacteria have been found in persons who have sustained injuries in marine environments; apparently, V. cholerae in water can penetrate broken skin and cause infection.

Transmission of cholera

Cholera is endemic in several areas of the world, including parts of India and Bangladesh. From these areas, cholera has been disseminated throughout the world during several pandemics, or worldwide outbreaks. In the United States, a cholera pandemic that lasted from 1832 until 1849 killed 150, 000 people; in 1866, another cholera pandemic killed 50, 000 U.S. citizens. The most recent pandemic, which began in the 1960s and lasted until the early 1980s, involved Africa, Western Europe, the Philippines, and Southeast Asia. Smaller outbreaks, such as the Rwanda epidemic of 1994, are characteristic of wartime and famine conditions, in which large numbers of people concentrate in one place where sanitary conditions are poor to nonexistent.

Because of the nature of V. cholerae infection, past epidemics can lead to future epidemics. People recovering from cholera continue to shed the organism in their feces for weeks to months after the initial infection. These people are called convalescent carriers. Another kind of carrier, called a chronic carrier, continues to shed the bacteria for years after recovery. In both carrier types, no symptoms are present. With the ease of worldwide transportation, carriers can travel throughout the world, spreading V. cholerae wherever they go. If a carrier visits an area with less-than-ideal sanitary conditions or does not wash his or her hands after using the bathroom, the deadly V. cholerae bacteria can be easily transmitted.

Symptoms and treatment of cholera

Cholera is characterized by sudden onset. Within several hours or days after ingesting V. cholerae, severe diarrhea and vomiting occur. Fluid losses can be up to 4-5 gal (15-20 l) per day. As a consequence of this severe fluid loss, the eyes and cheeks can appear sunken, and the skin loses its pliancy.

Treatment of cholera involves the rapid replacement of fluid and electrolytes. Most persons can be treated using special rehydration formulations that utilize rice or grain as a base and are supplemented with appropriately balanced electrolytes. If a patient is too severely ill to drink even small, frequent sips, infusions of electrolytes and fluids may be necessary. Once fluid and electrolyte balance is restored, rapid reversal of symptoms occurs. Treatment with antibiotics, typically tetracycline, neutralizes the V. cholerae and decreases the number of bacteria passed into the stool.

Prevention

In the United States, sewage treatment and water purification plants are ubiquitous, and consequently,

KEY TERMS

Electrolyte —Compounds that ionize in a solution; electrolytes dissolved in the blood play an important role in maintaining the proper functioning of the body.

Endemic —Maintains a presence in a particular area or among a particular group of people.

Pandemic —Occurring on a worldwide scale or spread over an entire country or nation.

Toxin —A poisonous substance.

the incidence of cholera is low. Almost all cases of cholera in the U.S. are caused by improperly cooked shellfish. Experts recommend that all shellfish be boiled for 10 minutes; steaming does not kill V. cholerae. Raw shellfish should be avoided.

Another way to prevent cholera is to identify and treat cholera carriers in areas where cholera is endemic. Treating carriers would eliminate a major route of cholera transmission.

Currently, several cholera vaccines are being developed, but only one, Dukoral^®, is likely to be effective for long periods. Although not yet approved for use in the U.S., Dukoral is an oral vaccine, which is more easily delivered to populations in the developing world than injectable vaccines. Once an outbreak has occurred, Orochol-E^® is usually a more effective vaccine to prevent further spread of the disease. Neither vaccine is effective against a relatively new type of cholera bacteria that emerged in India and Bangladesh in the early 1990s known as Vibrio cholerae O139. Cholera outbreaks caused by V. cholerae O139 have since been reported in eleven other countries in Southeast Asia. For travelers to cholera-endemic areas, preventive measures rather than vaccines are often advised. Suggestions include drinking only boiled or chlorine- or iodine-treated water; avoiding ice; avoiding fruits and vegetables unless cooked thoroughly or peeled; and eating only thoroughly cooked seafood.

Resources

BOOKS

Coleman, William, and Alcamo, I. Edward. Cholera (Deadly Diseases and Epidemics). New York: Chelsea House, 2003.

Hayhurst, Chris. Cholera. New York: Rosen Publishing Group, 2001.

Hempel, Sandra. The Strange Case of the Broad Street Pump: John Snow and the Mystery of Cholera. Berkeley: University of California Press, 2006.

OTHER

“Cholera.” Centers for Disease Control and Prevention. <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/cholera_g.htm> (accessed November 25, 2006).

Cholera

What Is Cholera?

Is Cholera Common?

How Do People Contract Cholera?

What Happens to People Who Have Cholera?

How Can Cholera Be Prevented?

Resources

Cholera (KAH-luh-ruh) is an acute* infection of the small intestine* that can cause severe diarrhea (dye-uh-REE-uh).

*acute

describes an infection or other illness that comes on suddenly and usually does not last very long.

*small intestine

is the part of the intestine—the system of muscular tubes that food passes through during digestion—that directly receives the food after it passes through the stomach.

KEYWORDS

for searching the Internet and other reference sources

Dehydration

Diarrhea

Epidemics

Enteritis

Vibrio cholerae

What Is Cholera?

Cholera is an illness caused by the bacterium Vibrio cholerae, which is contracted by eating contaminated food or drinking contaminated water. The bacteria can cause serious diarrhea by producing a toxin that makes the intestines release more water and minerals than usual. The disease has a 1 to 5 day incubation period (the time between infection and when symptoms appear) and progresses very quickly. Most cases of cholera are mild, but in about 1 of 20 cases the disease is serious. If left untreated, severe cholera can lead to death from dehydration within hours. With treatment, the death rate is less than 1 percent.

Is Cholera Common?

Cholera has been rare in industrialized (or highly developed) countries such as the United States since the turn of the twentieth century, thanks to improved sanitation and water treatment. However, cholera is still common in other parts of the world, including India and southern Asia, parts of Africa, and Latin America.

In 1991, an epidemic* of cholera occurred in South America and some cases appeared in the United States shortly thereafter. Most cases of cholera reported in the United States can be traced to travel to an area where cholera is endemic*.

*epidemic

(eh-pih-DEH-mik) is an outbreak of disease, especially infectious disease, in which the number of cases suddenly becomes far greater than usual. Usually epidemics are outbreaks of diseases in specific regions, whereas worldwide epidemics are called pandemics.

*endemic

(en-DEH-mik) describes a disease or condition that is present in a population or geographic area at all times.

How Do People Contract Cholera?

Cholera is spread when people eat food or drink water that has been contaminated with feces (excreted waste) containing Vibrio cholerae. Risk factors for epidemics of cholera include unsanitary and crowded living conditions, war, famine (scarcity of food), and natural disaster. For example, following a natural disaster such as a hurricane or flood, supplies of drinking water can become contaminated. The disease is most frequently spread in areas with poor sanitation and water treatment facilities.

During outbreaks of the disease, cholera may spread by contact with the feces of an infected person; Vibrio cholerae can live in feces for up to 2 weeks. It also spreads when people use contaminated water for cleaning or waste disposal. Eating raw or undercooked shellfish can be another source of the illness because the bacteria can survive in slow-moving rivers and coastal waters. The few cases in the United States are typically caused by contaminated seafood from the Gulf of Mexico or seafood brought home by people who have traveled to other countries.

What Happens to People Who Have Cholera?

Signs and symptoms

The major symptom of cholera is diarrhea, which can be severe and cause up to a quart of fluid loss per hour from the body. Diarrhea caused by cholera is painless, with stools that are fishy smelling and watery, often with flecks of mucus* in them (these are sometimes called “rice water” stools, because they look like rice floating in water).

*mucus

(MYOO-kus) is a thick, slippery substance that lines the insides of many body parts.

Most cases of cholera are mild or moderate, and they can be difficult to distinguish from other causes of diarrhea. More serious cases can cause severe diarrhea, vomiting, and dehydration. Signs of dehydration include decreased urination, extreme tiredness, rapid heartbeat, dry skin, dry mouth and nose, thirstiness, and sunken eyes.

Concern Over Cholera

Until the late 1800s, cholera was a very real threat in the United States, and the numbers of cases often reached epidemic proportions. In 1849, the immigrant boat John Drew brought cholera to the city of Chicago, where 678 people died of the disease that year.

By 1870, cholera was no longer a major threat in the United States because of improved sanitation and water treatment. However, the disease continues to be a significant concern in other parts of the world. In 1961, a pandemic (an epidemic that occurs over a large geographic area) that began in Indonesia spread to Bangladesh, India, Iran, and Iraq by 1965. In 1970, cholera appeared in West Africa, where it had not been seen in 100 years. It eventually became endemic to most of the continent.

Eating raw or undercooked oysters, crabs, or shrimp that have come from polluted waters is one way to contract cholera. Outbreaks have been associated with seafood from the Gulf of Mexico. The disease associated with this type of cholera bacteria is less severe than that caused by types seen in Asia. U.S. Fish and Wildlife Service (Washington, D.C.)

Diagnosis

Because the symptoms of cholera are often identical to those of other illnesses that cause diarrhea, knowing that a person has traveled to a country where cholera is endemic is important in helping a doctor make the diagnosis. Blood and stool samples can be taken to look for signs of the bacteria.

Treatment

Treatment of cholera can be very simple and effective, especially if it is given soon after symptoms appear. Rehydration, or replenishing the body with fluids, is the most important part of treatment. This can be accomplished most effectively by drinking a mixture of sugar, salts, and clean water, known as an oral rehydration solution. The World Health Organization has an oral rehydration solution that is distributed worldwide through the efforts of the United Nations. In the United States, solutions can be bought or mixed at home. Such solutions replenish the fluid and salts lost by the body due to diarrhea and vomiting.

More serious cases of cholera may require intravenous (in-tra-VEE-nus) fluids, or fluids injected directly into a vein. Antibiotics, which are given in severe cases, can shorten the time that the symptoms last and help prevent spread of the disease to others.

Complications from cholera are usually the result of severe dehydration. Seizures*, abnormal heart rhythms, shock*, damage to the kidneys*, coma*, and death can occur. Children, especially infants, are more likely to develop complications than adults because they are more prone to developing severe dehydration and body mineral imbalances.

*seizures

(SEE-zhurs) are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.

*shock

is a serious condition in which blood pressure is very low and not enough blood flows to the body’s organs and tissues. Untreated, shock may result in death.

*kidneys

are the pair of organs that filter blood and remove waste products and excess water from the body in the form of urine.

*coma

(KO-ma) is an unconscious state in which a person cannot be awakened and cannot move, see, speak, or hear.

How Can Cholera Be Prevented?

Steps people can take to prevent cholera when traveling or after a natural disaster include:

• drinking only bottled water, water that has been boiled or treated with chlorine or iodine, or bottled, carbonated beverages
• eating only food that has been thoroughly cooked and is still hot
• not eating raw fruit or vegetables unless they have been peeled
• avoiding food and drinks sold by street vendors
• avoiding raw or undercooked seafood
• not bringing seafood from abroad back to the United States.

Vaccines* for cholera exist, but their effectiveness is short lived and none are provided or recommended in the United States.

*vaccines

(vak-SEENS) are preparations of killed or weakened germs, or a part of a germ or product it produces, given to prevent or lessen the severity of the disease that can result if a person is exposed to the germ itself. Use of vaccines for this purpose is called immunization.

See also

Resources

Organizations

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC is the U.S. government authority for information about infectious and other diseases. It has a fact sheet about cholera at its website.

Telephone 800-311-3435 http://www.cdc.gov

World Health Organization (WHO), Avenue Appia 20, 1211 Geneva 27, Switzerland. WHO’s communicable disease surveillance and response division posts a global cholera update at its website to report numbers of cholera cases and deaths worldwide.

Telephone 011-41-22-791-2111 http://www.who.int

CHOLERA

Cholera is an acute diarrheal illness caused by a bacterium, Vibrio cholerae. There are several environmental strains of Vibrio cholerae, which are found mainly in brackish waters and marine environments, but only two strains are responsible for cholera epidemics in humans, serogroups O1 and O139.

The first described cholera pandemic was in Europe from 1817 to 1823. However, the disease was known in Asia prior to that, with the first possible descriptions dating back as far as 2,000 years ago in India and China. Since that first pandemic there have been a total of seven pandemics. The cholera outbreaks that occurred in London, England in 1849 and 1854 are important in the history of the disease. John Snow, a physician, recognized that cholera was spread via water contaminated with human waste when he identified the source of the London outbreak as the Broad Street water pump. This discovery stimulated the future development of adequate water and sewage systems, which led to the control of many infectious diseases.

The seventh pandemic started in Sulawesi, an island in Indonesia, in 1961 and then spread rapidly through Asia and the Middle East. In 1970, for the first time in over one hundred years, cholera was found in West Africa. In 1991, cholera appeared in Peru and quickly spread throughout the remainder of South and Central America. As was the case with Africa, cholera had not been seen in the western hemisphere for over one hundred years. As of 2001, the seventh cholera pandemic showed no signs of abating.

Cholera is acquired by ingestion of V. cholerae in water, seafood, or other foods that have been contaminated by human excrement. The incubation period can range from a few hours to five days, depending on the inoculum size and the underlying health of the person. Cholera can cause a spectrum of disease, from no clinical symptoms to a mild diarrheal illness or a severe fulminant illness resulting in death. The diarrhea is caused by an enterotoxin produced by the V. cholerae that stimulates the small intestine to secrete large volumes of fluid and electrolytes. Some factors that predispose to severe disease include having blood group O, low gastric acid levels, and malnutrition. The very young and the very old are at particular risk for severe disease. Persons living in endemic areas appear to develop some natural immunity to the infection.

In symptomatic infections, there is an abrupt onset of copious diarrhea, often accompanied by abdominal cramps and vomiting. The diarrhea is typically watery and clear with mucous flecks— often described as "rice water stools." It is unusual for fever to develop. Uncomplicated cholera is a self-limited disease that resolves in three to six days. In more severe cases, fluid losses from diarrhea can amount to over 20 liters a day and can lead to profound dehydration that produces weakness, muscle cramping, loss of skin turgor, and sunken eyes and cheeks. If the fluid losses are not rapidly corrected, death results. The fatality rate can be over 50 percent in cases of severe cholera; however, with prompt and adequate rehydration the death rate may be as low as 1 to 2 percent.

The infection is diagnosed by identification of V. cholerae bacteria in stool. The organism can be grown in the laboratory on special alkaline culture media. It appears microscopically as curved, gramnegative rods. A clinical diagnosis can be made in severe cases if a patient presents with profuse, watery diarrhea in an endemic region. There are few other illness that cause such copious diarrhea.

The mainstay of treatment is fluid replacement, either intravenously or orally. In very severe cases, intravenous fluid replacement should be used. When fluids are administered by mouth, it is important to use an oral rehydration solution that contains the correct mix of sugars and electrolytes.

Antibiotics can be used to shorten the duration of illness by several days. Tetracycline, furazolidone, or doxycycline are all effective.

Prevention of cholera depends upon good sanitation and hygiene, including treatment of water supplies, adequate sewage control, and strict hygiene in food preparation. Good food preparation involves hand washing before contact with food, thorough cooking of food, eating food while it is still hot, and not allowing cooked food come into contact with raw foods or with water or ice.

There are several vaccines currently available to prevent cholera. The original cholera vaccine was a parenteral-killed preparation that provided about 50 to 60 percent protection and was only effective for a period of three to six months. This vaccine is no longer recommended for use. The World Heath Organization currently advocates the use of a killed whole cell V. cholerae O1 vaccine (WC/rBS), which is combined with one of the toxin subunits and is given in two doses one week apart. This newer vaccine has been shown to confer 85 to 90 percent protection for six months. The vaccine can be used to prevent a cholera outbreak in a population felt to be at high risk of an out-break, such as the inhabitants of refugee camps. It can also be offered to travelers going to high-risk regions. Another recently developed effective vaccine is the oral, single dose, live attenuated V. cholerae strain, devoid of the A toxin subunit (Mutachol), that provides from 62 to 100 percent protection for about six months. The level of protection varies for different cholera biotypes.

A concern about future cholera outbreaks is the possible emergence of new biotypes. Until 1992, the only strain of cholera identified as causing epidemics in humans was V. cholerae O1. That year a new serotype, O139, emerged in India. Neither previous exposure to O1 cholera, nor vaccination with current vaccines, confers protection against O139. Because V. cholerae exists naturally in brackish waters, and because of the possibility of new biotypes emerging, it is unlikely that cholera will ever be eradicated as a human pathogen. Good hygiene and sanitation are the best strategies we have for control of this disease.

Martha Fulford

Jay Keystone

(see also: Communicable Disease Control; Epidemics; Waterborne Diseases )

Bibliography

Raufman, J. P. (1997). "Cholera." American Journal of Medicine 104:386–394.

Reeves, P. R., and Lan, R. (1998). "Cholera in the 1990s." British Medical Bulletin 54 (3):611–623.

Ryan, E. T., and Calderwood, S. B. (2000). "Cholera Vaccines." Clinical Infectious Diseases 31:561–565.

Sanchez, J. L., and Taylor, D. N. (1997). "Cholera." Lancet 349.

Scheld, W. M.; Craig, W. A.; and Hughes, J. M., eds. (1998). "Cholera and Vibrio Cholerae: New Challenges from a Once and Future Pathogen." In Emerging Infections 2. Washington, DC: ASM Press.

World Health Organization. Vaccines, Immunization and Biologicals—Cholera. Available at http://www.who.int/vaccines/intermediate/cholera.htm.

—— (2000). Fact Sheet 107: Cholera. Geneva: WHO.