Cholera
Cholera
Disease History, Characteristics, and Transmission
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