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Cholera

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Biology

Cholera is one of the most known bacterial infectious diseases. Like other infectious diseases such as Tuberculosis (TB), it is caused and spread by a bacterial pathogen that enters and infects the human body causing illness.

Despite being completely curable, many people still die of cholera in developing countries. According to the World Health Organisation (WHO), cholera remains a threat to global public health and a clear indicator of inequality between the developed and developing world.

What is cholera?

Cholera is a disease characterised by an infection of the intestine caused by the pathogenic bacteria Vibrio Cholerae. In severe cases, this infectious disease can lead to diarrhoea and death within hours if left untreated. The WHO and researchers estimate that around 3,000,000 cases and 100,000 avoidable deaths from cholera happen every year, almost exclusively in developing countries in Asia, Africa, and Latin America. Cholera infection numbers have remained high for the past few years. According to the WHO, these are likely to be underestimated as many countries may not fully report outbreaks for fear of impacts in their economies (tourism/trade).

Understanding how cholera transmits between people is essential to understand why it is more prevalent in developing countries. Direct personal cholera transmission is unlikely as large amounts of this bacteria typically exit the body of infected people through their faeces. The bacteria present in faeces can contaminate water and food that comes into contact with it. In other words, this infectious disease is water and food-borne. Vibrio Cholerae survives and spreads via contaminated water and food. Proper access to sanitation and basic hygiene rules are the critical factors in reducing the transmission chain of this pathogen. The infrastructure to help achieve this tends to lack more in developing countries, so cholera is more prevalent in these regions.

To learn more about how pathogens can spread and cause illness, check out our explanation on Infectious Disease.

Cholera is a diarrhoeal infectious disease caused by the ingestion of water or food contaminated with the bacterial pathogen Vibrio Cholerae. Cholera affects the small intestine wall disrupting its function.

Causes of cholera

Cholera disease is caused by the infection resulting from the bacteria Vibrio Cholerae. People contract cholera by eating food or drinking water contaminated with Vibrio Cholerae. This pathogen first passes through the stomach to reach its site of action in the wall of the small intestine. In the small intestine, Vibrio Cholerae multiplies and releases choleragen, a toxin that affects the epithelium wall of the intestine. Choleragen can cause dramatic loss of fluids with water and salts leaving the blood. It causes diarrhoea which can be fatal if left untreated.

There are only two strains of Vibrio Cholerae capable of causing cholera outbreaks: the O1 and O139 strains. These strains cause the same symptoms and illness, but the O139 strain appears more virulent. Exposure to one strain does not seem to provide immunity to the other.

There have been seven worldwide outbreaks (pandemics) of cholera since the 19th century, killing millions of people on all continents. The O1 strain was the first cholera-causing strain to be identified and is thought to have spread from its original reservoir in the delta of the Ganges river in India. The O1 strain continues to cause most of the recent cholera outbreaks. The last cholera pandemic started in South Asia in 1961 and has spread across the developing world to become endemic in many places. The 0139 strain was only identified according to the WHO in 1992 in Bangladesh. Despite fears that the 0139 strain could cause a more aggressive outbreak and cholera pandemic, that appears not to have happened.

Cholera symptoms

Cholera infection is mild to moderate or even asymptomatic amongst most people after becoming infected with the toxigenic bacteria Vibrio Cholerae. However, this doesn’t mean that these people are not capable of infecting others. Asymptomatic individuals can still pass the bacteria through their faeces 1-10 days after infection, potentially spreading the bacteria further into the environment.

Asymptomatic individuals carry the pathogen of disease but present no clinical symptoms.

According to the WHO, about 1 in 10 people who become infected with cholera will develop severe symptoms. Cholera affects adults and children equally. Symptom onset can take anywhere from a few hours to 5 days (the incubation period) after ingestion of the cholera bacteria but usually takes 2-3 days. This minority of people will experience severe watery diarrhoea (also known as ‘rice water’ diarrhoea), dehydration, shock, vomiting, weakness, and leg cramps. The associated rapid loss of body fluids (water and salts) can be fatal, killing within 24 hours if these fluids aren’t replaced.

The incubation period is the time between the initial exposure of the pathogen to the first appearance of clinical symptoms.

Cholera transmission

Cholera bacteria are passed on through the faeces of an infected person. These feces can contaminate water supplies in regions with inadequate water management/treatment and sanitation facilities. Infected people who come into contact with food or cooking utensils without washing their hands can inadvertently contaminate food supplies. Poor hygiene is a contributing factor in further spreading the bacteria.

As mentioned before, individuals contract cholera by ingesting water/food that has been contaminated with cholera bacteria. Casual contact with an infected person is therefore not a risk factor for becoming infected and ill with cholera.

Eating raw shellfish has been shown to lead to cholera infection even in developed countries like the US, where people have contracted this disease from eating raw/undercooked seafood from the Gulf of Mexico. Filter-feeders like oysters or mussels are in particular sources of infection because they concentrate the bacteria when the water body they live in becomes contaminated with raw sewage that has Vibrio Cholerae.

Cholera transmission is therefore much more common in urban slums in developing countries or refugee camps because of unsatisfactory access to clean water supplies or sanitation infrastructure. Cholera is, therefore, rarely found in developed countries where there is a significant investment in clean piped water and sewage treatment facilities that kill any bacteria through the use of chlorine.

Cholera outbreaks are a serious concern whenever a humanitarian crisis happens following natural disasters. These events can devastate populations and destroy critical infrastructure like sanitation facilities, leading to outbreaks of diarrhoeal diseases such as cholera. An example is the 2010 Haiti earthquake.

Treatment and prevention of cholera

Controlling cholera outbreaks requires several strategies, including treating infected people, using oral cholera vaccines, increasing water sanitation and hygiene, and surveillance strategies.

Surveillance strategies are essential to contain outbreaks quickly and require effective and fast diagnostic approaches. Cholera is diagnosed by identifying cholera bacteria in a stool sample or rectal swab, usually sent to a lab. A quick diagnosis is essential to provide a rapid treatment that can be life-saving. According to the WHO, quick access to proper treatment keeps cholera’s case-fatality rate below 1%.

Treatment of cholera is very cheap and straightforward. People with mild or moderate symptoms usually receive oral rehydration therapy. This is a solution of salts and glucose that rehydrates the body, thus diminishing the impact of the fluid losses caused by diarrhoea. Patients with more severe dehydration usually receive intravenous fluids and antibiotics.

Tetracycline antibiotics, such as doxycycline, are effective against cholera infection.

Preventative steps are also essential when visiting areas with cholera epidemics. Basic hygiene and water consumption precautions can significantly reduce the risk of becoming infected. According to the Centres for Disease Control and Prevention (CDC), some precautions include only drinking bottled water, disinfecting your own water (e.g., boiling or filtering), washing hands thoroughly before eating, cooking, or handling food, eating pre-packaged hot food, and never raw/undercooked food.

Oral cholera vaccines are among the additional strategies that can be used in cholera outbreak scenarios to help fight the disease. The WHO has approved three different vaccines, but they only provide short-term protection. These vaccines are not 100% protective and should not be used instead of other preventative measures like precautions over contaminated food and water.

Long-term resolution and eradication of cholera disease will require the development of infrastructure for sanitation and clean water supplies to areas of sub-standard housing in developing countries. There should be universal access to safe drinking water and proper sanitation facilities that encourage good hygiene practices.

Cholera - Key takeaways

  • Cholera is a diarrhoeal infectious disease caused by the ingestion of water or food contaminated with the bacterial pathogen Vibrio Cholerae.
  • Cholera infection is mild to moderate or even asymptomatic amongst most people. Severe symptoms include watery diarrhoea, dehydration, shock, vomiting, and weakness.
  • Cholera bacteria are passed on through the faeces of an infected person. The faecal matter can contaminate water/food supplies in regions with inadequate sanitation facilities, such as in developing countries or following humanitarian crises (natural disasters).
  • Treatment of cholera is very cheap and simple. Oral rehydration therapy (solution of salts and glucose) is used to replenish the lost bodily fluids caused by diarrhoea.

Cholera

Cholera is a diarrhoeal infectious disease caused by the ingestion of water or food contaminated with the bacterial pathogen Vibrio Cholerae.

Ingestion of food or water contaminated with Vibrio Cholerae. 

Watery diarrhoea (also known as ‘rice water’ diarrhoea), dehydration, shock, vomiting, weakness, and leg cramps.

Cholera is a contagious infectious disease but direct person-to-person transmission is unlikely. Cholera infection usually happens by coming into contact with water or food that has been contaminated with faecal matter from a person with cholera.

Water/food supplies contaminated with faecal matter containing Vibrio Cholerae (cholera bacteria).

Final Cholera Quiz

Question

What kind of pathogen infection results in cholera?

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Answer

Bacteria (Vibrio Cholerae)

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Question

There is no vaccine for cholera. True or False.

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Answer

False

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Question

Why is cholera more widespread in developing countries?


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Answer

Lack of access to safe drinking water and proper sanitation facilities.

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Question

Cholera is water and food-borne. What does this mean?

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Answer

Cholera bacteria can survive in water and food and be transmitted through the ingestion of contaminated water/food.

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Question

Why is direct person-to-person transmission of cholera unlikely? 

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Answer

Cholera bacteria exits the body of an infected person through its faeces.

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Antibiotics are always recommended for cholera infections. True or False 


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Answer

False

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Symptoms of cholera include 

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Answer

Diarrhoea and vomiting

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What is the main symptom of cholera?

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Answer

Diarrhoea

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Question

Why is oral rehydration therapy the main treatment strategy for cholera?

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Answer

It provides the body with the fluids it lost as a result of cholera diarrhoea.

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Which of the following actions should you not do when travelling to an area with a cholera outbreak?


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Answer

Eat shellfish

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How many strains of Vibrio Cholerae are there?

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Answer

There are many different strains but only two can cause cholera.

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What events cause particular concern over possible cholera outbreaks?

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Answer

Natural disasters

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What is oral rehydration therapy?

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Answer

A solution composed of salts and glucose that is either ingested or injected into a patient with cholera.

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What food can concentrate the cholera bacteria very easily?


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Answer

Filter-feeder shellfish like oysters or muscles.

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Question

Why is a quick diagnosis of cholera important?

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Answer

In severe cases, people can die within 24hours of cholera symptom onset.

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