What is cholera?
By the start of the 20th century, there had been six major cholera pandemics. The world is now fighting its seventh, caused by a new strain of the Vibrio cholerae bacterium, El Tor.
Epidemics involving this strain started in 1961 in Indonesia, spreading rapidly elsewhere in eastern Asia, and from there to India and Bangladesh, the USSR, Iran and Iraq. Cholera is rare in developed countries with a reliable public water supply and good drainage. Only 35 cases of cholera were reported in Europe in 2000 and only nine in North America.
What is the history of cholera?
Cholera has likely been affecting humans for many centuries. Reports of cholera-like disease have been found in India as early as 1000 AD. Cholera is a term derived from Greek khole (illness from bile) and later in the 14th century to colere (French) and choler (English). In the 17th century, cholera was a term used to describe a severe gastrointestinal disorder involving diarrhea and vomiting. There were many outbreaks of cholera, and by the 16th century, some were being noted in historical writings. England had several in the 19th century, the most notable being in 1854, when Dr. John Snow did a classic study in London that showed a main source of the disease (resulting in about 500 deaths in 10 days) came from at least one of the major water sources for London residents termed the “Broad Street pump.” The pump handle was removed, and the cholera deaths slowed and stopped. The pump is still present as a landmark in London. Although Dr. Snow did not discover the cause of cholera, he did show how the disease could be spread and how to stop a local outbreak. This was the beginning of modern epidemiologic studies. The last reference shows the map Dr. Snow used to identify the pump site.
V. cholerae was first isolated as the cause of cholera by Filippo Pacini in 1854, but his discovery was not widely known until Robert Koch (who also discovered the cause of tuberculosis), working independently 30 years later, publicized the knowledge and the means of fighting the disease. The history of cholera repeats itself. The U.S. National Library of Medicine houses original documents about multiple cholera outbreaks in the U.S. from the 1820s to the 1900s, with the last large outbreak in 1910-1911. Since the 1800s, there have been seven cholera pandemics (worldwide outbreaks). The seventh pandemic of cholera started in 1961 and lasted until 1975; some researchers think the occasional outbreaks (even up to the present time) represent remnants of the seventh pandemic.
Cholera riots occurred in Russia and England (1831) and in Germany (1893) when the people rebelled against strict government isolation (quarantines) and burial rules. In 2008, cholera riots broke out in Zimbabwe as police tried to disperse people who tried to withdraw funds from banks and were protesting because of the collapse of the health system that began with a cholera outbreak. Similar but less violent public protests have occurred when yellow fever, typhoid fever, and tuberculosis quarantines have been enforced by health authorities.
Multiple outbreaks continue into the 21st century, with outbreaks in India, Iran, Vietnam, and several African countries over the last 10 years. Some recent outbreaks occurred in Haiti and Nigeria in 2010-2011, and South Sudan, Tanzania, Iraq, Kenya, and Cuba in 2015-2016, and Yemen in 2017-18. Since 2017-2018, the WHO has listed 1,084,191 suspected cases of cholera with 2,267 associated deaths in war-torn Yemen.
Why is cholera history repeating itself? The answer can be traced back to Dr. Snow’s studies that show a source (water-borne or occasionally food) contaminated with V. cholerae can easily and rapidly transmit the cholera-causing bacteria to many people. Until safe, clean water and food is available to all humans, it is likely that cholera outbreaks will continue to happen.
Causes of cholera
Cholera is a form of gastroenteritis caused by a toxin produced by the bacterium Vibrio cholerae.
The bacterium is part of the flora of brackish water and estuaries – it’s when this water gets into the drinking supply that an outbreak can start.
It causes severe diarrhea and vomiting, and patients, particularly children and the elderly, are vulnerable to dangerous dehydration as a result.
An outbreak of cholera can spread quickly in areas where there is poor sanitation and where water supplies can be tainted. It’s a common problem in disaster areas where water supplies are disrupted.
Most people infected with cholera don’t actually get ill. Despite this, they are contributing to the problem because the bacteria remain in their faeces for up to a fortnight. It’s only rarely spread by person-to-person contact.
Symptoms of cholera
In most cases symptoms are so mild they may go unnoticed. But in about five per cent there is profuse watery diarrhoea, vomiting and leg cramps.
Life-threatening dehydration can occur very rapidly. Without treatment, severe infection has a mortality rate of 30 to 50 per cent. In vulnerable people such as the young or elderly, cholera can prove fatal within hours.
Most symptomatic cases are hard to distinguish from other illnesses that cause diarrhoea, but it’s important to make a diagnosis as quickly as possible to prevent dehydration.
According to the World Health Organization, a well-organised response to cholera can reduce death rates to one per cent. An unprepared community, however, will experience many times this death rate.
Risk factors of Cholera
Everyone is susceptible to cholera, with the exception of infants who derive immunity from nursing mothers who have previously had cholera. Still, certain factors can make you more vulnerable to the disease or more likely to experience severe signs and symptoms. Risk factors for cholera include:
- Poor sanitary conditions. Cholera is more likely to flourish in situations where a sanitary environment — including a safe water supply — is difficult to maintain. Such conditions are common to refugee camps, impoverished countries, and areas devastated by famine, war or natural disasters.
- Reduced or nonexistent stomach acid (hypochlorhydria or achlorhydria). Cholera bacteria can’t survive in an acidic environment, and ordinary stomach acid often serves as a first line defense against infection. But people with low levels of stomach acid — such as children, older adults, and people who take antacids, H-2 blockers or proton pump inhibitors — lack this protection, so they’re at greater risk of cholera.
- Household exposure. You’re at significantly increased risk of cholera if you live with someone who has the disease.
- Type O blood. For reasons that aren’t entirely clear, people with type O blood are twice as likely to develop cholera compared with people with other blood types.
- Raw or undercooked shellfish. Although large-scale cholera outbreaks no longer occur in industrialized nations, eating shellfish from waters known to harbor the bacteria greatly increases your risk.
Complications of Cholera
Cholera can quickly become fatal. In the most severe cases, the rapid loss of large amounts of fluids and electrolytes can lead to death within two to three hours. In less extreme situations, people who don’t receive treatment may die of dehydration and shock hours to days after cholera symptoms first appear.
Although shock and severe dehydration are the most devastating complications of cholera, other problems can occur, such as:
- Low blood sugar (hypoglycemia). Dangerously low levels of blood sugar (glucose) — the body’s main energy source — may occur when people become too ill to eat. Children are at greatest risk of this complication, which can cause seizures, unconsciousness and even death.
- Low potassium levels (hypokalemia). People with cholera lose large quantities of minerals, including potassium, in their stools. Very low potassium levels interfere with heart and nerve function and are life-threatening.
- Kidney (renal) failure. When the kidneys lose their filtering ability, excess amounts of fluids, some electrolytes and wastes build up in your body — a potentially life-threatening condition. In people with cholera, kidney failure often accompanies shock.
When to see a doctor
The risk of cholera is slight in industrialized nations, and even in endemic areas you’re not likely to become infected if you follow food safety recommendations. Still, sporadic cases of cholera occur throughout the world. If you develop severe diarrhea after visiting an area with active cholera, see your doctor.
If you have diarrhea, especially severe diarrhea, and think you may have been exposed to cholera, seek treatment right away. Severe dehydration is a medical emergency that requires immediate care regardless of the cause.
Treatment of cholera
Treating the condition, or rather alleviating the severe life-threatening effects, requires only simple measures. Normally, rehydration salts (mixed with clean water into a drink) are the only treatment given, although severely dehydrated patients may need intravenous fluids. However, the clean water and rehydration salts required are often in short supply in areas where they are needed most.
Antibiotics can reduce the amount of diarrhoea. There are two oral cholera vaccines, but these are mainly aimed at travellers rather than wider use in a community stricken by the illness.
Control of an epidemic is difficult in a community unless clean water supplies can be restored. Systems for hygienic disposal of human waste also need to be brought in. Cooking practices need to be made as safe as possible – where practicable, food needs to be cooked thoroughly and eaten while hot, and raw fruit and vegetables avoided unless they are peeled first.
Hand-washing after going to the toilet and before preparing food is a vital measure to prevent the spread of the disease.
Oral cholera vaccines are safe and effective but must not be considered as a substitute for basic preventative measures such as clean water and sanitation.
Prevention of Cholera
There is a vaccine for cholera. Both the CDC and the World Health Organization have specific guidelines for who should be given this vaccine.
You can protect yourself and your family by using only water that has been boiled, water that has been chemically disinfected, or bottled water. Be sure to use bottled, boiled, or chemically disinfected water for the following purposes
- Preparing food or drinks
- Making ice
- Brushing your teeth
- Washing your face and hands
- Washing dishes and utensils that you use to eat or prepare food
- Washing fruits and vegetables
To disinfect your own water, boil it for one minute (or 3 minutes at higher elevations) or filter it and use a commercial chemical disinfectant. You should also avoid raw foods, including the following:
- Unpeeled fruits and vegetables
- Unpasteurized milk and milk products
- Raw or undercooked meat or shellfish
- Fish caught in tropical reefs, which may be contaminated
If you develop severe, watery diarrhea and vomiting — particularly after eating raw shellfish or traveling to a country where cholera is epidemic — seek medical help immediately. Cholera is highly treatable, but because dehydration can happen quickly, it’s important to get cholera treatment right away.
Hydration is the mainstay of treatment for cholera. Depending on how severe the diarrhea is, treatment will consist of oral or intravenous solutions to replace lost fluids. Antibiotics, which kill the bacteria, are not part of emergency treatment for mild cases. But they can reduce the duration of diarrhea by half and also reduce the excretion of the bacteria, thus helping to prevent the spread of the disease.
For adults traveling to areas affected by cholera, a vaccine is now available in the United States. The Food and Drug Administration recently approved Vaxchora, a vaccine for the prevention of cholera. It is a liquid dose taken by mouth at least 10 days before travel.
A few countries offer oral vaccines as well. Contact your doctor or local office of public health for more information about these vaccines. Keep in mind that no country requires immunization against cholera as a condition for entry.
Hygiene promotion and social mobilization
Health education campaigns, adapted to local culture and beliefs, should promote the adoption of appropriate hygiene practices such as hand-washing with soap, safe preparation and storage of food and safe disposal of the feces of children. Funeral practices for individuals who die from cholera must be adapted to prevent infection among attendees.
Further, awareness campaigns should be organised during outbreaks, and information should be provided to the community about the potential risks and symptoms of cholera, precautions to take to avoid cholera, when and where to report cases and to seek immediate treatment when symptoms appear. The location of appropriate treatment sites should also be shared.
Community engagement is key to long term changes in behavior and to the control of cholera.
Frequently Asked Questions About Cholera
What is cholera?
Cholera is an acute diarrheal disease that in severe cases rapidly leads to dehydration and death if appropriate treatment is not provided immediately.
Cholera is a disease in which the bacterium Vibrio cholerae colonizes the small intestine and produces a toxin which leads to massive secretion of water and salts. This huge amount of fluid from the intestinal cells is much more than the intestine can reabsorb and so the fluid comes pouring out as watery diarrhea. The loss of fluids is so great that the patient can quickly become severely dehydrated, go into shock, and die within a few hours. The diarrhea fluid is teeming with huge numbers of the bacteria and these can rapidly spread to others, leading to epidemics.
What are the symptoms of cholera?
Cholera patients commonly present with diarrhea and vomiting. In severe cases, diarrhea is voluminous, resulting in dehydration and shock within a few hours.
Symptoms can range from mild diarrhea to very severe diarrhea. Severe cases are generally accompanied with severe vomiting, weakness, and shock. Muscle cramps in the legs and arms are also common because of the electrolyte imbalance. With shock, the patient may lose consciousness and this may lead to death.
What causes cholera?
The causative organism, Vibrio cholerae, is a gram-negative, comma-shaped bacillus known to have more than 200 serogroups. Only serogroups O1 and O139 have been associated with epidemics.
The causative bacterium (Vibrio cholerae) produces a toxin called cholera toxin which stimulates adenylate cyclase, increasing the level of intracellular cyclic AMP, which leads to the fluid secretion from intestinal cells that is much faster than it can be reabsorbed. Thus, the disease is actually caused by the toxin rather than the bacteria itself.
Who is most susceptible?
Cholera transmission occurs where there is unsafe water and poor sanitation. In areas where cholera is common, children aged <5 years have the highest rates of infection, but all age groups are at risk. Household contacts of cholera patients are at increased risk of developing the disease.
How is the disease transmitted?
Ingestion of fecally contaminated water is the most common source of transmission of cholera; therefore, it can easily spread in highly populated communities where access to clean water and sanitation are poor and when hygiene is compromised by insufficient hand washing and during food preparation. Cholera may also be transmitted via contaminated shellfish and food.
Are there mild and severe cases of cholera, or are they all the same intensity?
Most cholera infections (about 80%) are mild or unapparent. Among those who are infected, some develop severe dehydration from profuse, acute, watery diarrhea.
After an incubation period of 1-3 days, about 20% will develop diarrhea which may be severe, along with severe vomiting. As the illness progresses, the stools become like water with little flecks of mucus (called rice-water stool). The diarrhea is usually painless and may have a fishy smell. Patients may also have severe muscle cramps and spasms which can be very painful.
What exactly do the bacteria do to cause such severe diarrhea?
If a large enough dose of the bacteria is ingested and survives the acidity of the stomach, the bacteria then colonize the small intestine where they release cholera toxin. This toxin triggers mechanisms which eventually leads to massive purging of electrolyte-rich fluid in the small intestine that exceeds the absorptive capacity of the colon and is expelled as diarrhea. This loss of fluid and depletion of electrolytes can lead to rapid dehydration.
After ingestion of a large enough dose of the bacteria that are able to survive the gastric acidity, the Vibrio organisms then colonize mucosal cells of the small intestine. During this time, the organisms release cholera toxin that bind to the small intestinal epithelial cells. The release of the A subunit of the cholera toxin stimulates the enzyme system of the intestinal cells leading to the increase in chloride secretion by the crypt cells, which in turn leads to inhibition of absorption of sodium and chloride by the microvilli. These events eventually lead to massive purging of electrolyte-rich isotonic fluid in the small intestine that exceeds the absorptive capacity of the colon, resulting in rapid dehydration and depletion of electrolytes, including sodium, chloride, bicarbonate, and potassium.
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