Cholera is an infectious disease caused by the bacterium Vibrio cholerae.  It infects the small intestine.

There are many types (strains) of the Vibrio cholera bacteria.  Some of them cause more serious illnesses than others.  Because of this, some people who get cholera have no symptoms; others have symptoms that are not very bad, and others have very bad symptoms.

The most common symptom is large amounts of watery diarrhea.  In the worst cases, diarrhea can be so bad that people can die in a few hours from dehydration.

Cholera is a very old disease.  Writings about cholera (written in Sanskrit) have been found from the 5th century BC.  Throughout history, there have been many outbreaks and epidemics of cholera.

Cholera still affects many people throughout the world.  Estimates from 2010 say that between 3 million and 5 million people get cholera every year, and 58,000–130,000 people die from the disease every year.  Today, cholera is considered a pandemic.  However, it is most common in developing countries, especially in children.

Cause
People usually get cholera by eating food or drinking water that is unclean.  When people have cholera, they have a lot of diarrhea, and the cholera bacteria stays alive in their feces.  In developing countries, often there is not good sanitation.  Cholera can spread if this diarrhea gets into water that other people use.  For example, if sewage (human waste) gets into a river, people can get cholera if they:
 Drink the water from the river.
 Eat food that they have washed in the river.
 Eat fish that live in the river, if they are not cooked well enough to kill the cholera bacteria.
This is the most common cause of cholera in developed countries.  People eat seafood like oysters that were taken from waters with the cholera bacteria in them and sent to stores in developed countries.

Cholera is very rarely spread directly from person to person.

Signs and symptoms 

Cholera's main symptoms are bad diarrhea and vomiting clear fluid.  These symptoms usually start suddenly.  They start half a day to five days after the person gets infected.  (This is called cholera's "incubation period".)

If they do not get treatment, about half of people with serious cholera die.  People with bad cholera may have so much diarrhea that they do not have enough water and electrolytes (salts) left in their bodies to survive.  Cholera has been nicknamed the "blue death" because a person dying of cholera may lose so many body fluids that their skin turns bluish-gray.

Other symptoms may include:

 Lethargy (having no energy)
 Eyes that look sunken into the head, dry mouth, and saggy skin (from dehydration)   
 Changes in breathing
 Confusion
 Hypotension (low blood pressure)
 Tachycardia (fast heart rate)
 Shock caused by dehydration (called hypovolemic shock)
 Seizures (especially in children)
 Coma, especially in children

Prognosis
If people with cholera get good, quick medical treatment, less than 1% die from the disease.  However, if cholera is not treated, at least half of people with the disease (50% to 60%) die.

Some strains of the Vibrio cholera bacteria have different genes than others, which make them more dangerous.  These more dangerous strains of cholera bacteria caused the 2010 epidemic in Haiti and the 2004 outbreak in India.  A person who gets these strains of cholera can die within two hours of getting sick.  This means there is very little time to get the person treated.

Treatment 

There are antibiotics for cholera. There are various treatments which can help.  For example:
 Giving fluids to treat dehydration, either by mouth or through a needle placed into a vein (intravenously).
 Giving important electrolytes like potassium and sodium chloride (salt)
 Giving antibiotics.  These make symptoms go away faster and not be so bad.  However, people may recover without them if they are not too dehydrated. Some advice is that antibiotics are suggested for people who have bad cholera and are dehydrated.
 Patients should keep eating; this helps their intestines return to normal.

Prevention

Individuals 

There is a cholera vaccine that can be taken by mouth.  It provides some protection from cholera for about six months.

People can also do some other things to prevent cholera.  For example:
 Wash their hands with soap and/or ash after using the toilet, and before touching food or eating.
 Sterilize (remove germs from) all water used for drinking, washing, or cooking.  The best and least expensive ways to do this are to boil water or to add chlorine.  If this is not possible, using a cloth filter for water is better than nothing.
 Wash all fruits and vegetables using safe water.  Peel fresh fruits before eating them.
 Not put their untreated feces in rivers, oceans, or anywhere in the open environment. This can be avoided by using dry toilets, especially if governments do not properly treat sewage.
 Follow all suggestions from public health agencies like the World Health Organization and the Centers for Disease Control and Prevention about how to prevent spreading cholera (or other diseases).

Governments

Governments could stop outbreaks or epidemics from happening by improving sanitation.  For example, cholera is very uncommon in developed countries because they have good sanitation and because they add chemicals to their water to kill germs.  Even after people start to get cholera, it is possible for governments to stop the disease from spreading, though:
 Sterilization:  Any material that touched a cholera patient should be  cleaned with disinfectant and washed in hot water, using chlorine bleach if possible.  Hands that touched cholera patients or their things, like clothing or blankets, should be carefully cleaned and disinfected with water that has chlorine in it, or with other effective antimicrobial agents (chemicals that will kill bacteria).
 Sewage: Proper treatment can kill enough cholera bacteria for wastewater to go back into the environment. Dry toilets can be promoted where sewage treatment is not so good.
 Sources: Warnings about possible cholera in the water should be posted around contaminated water sources, with directions on how to kill the bacteria in the water through things like boiling or adding chlorine for possible use.

History 

Cholera probably started in the Indian subcontinent.  As early as the 5th century BC, people in the Ganges River delta area wrote about cholera.  The disease first spread to Russia in 1817 by trade routes (over both land and sea).  Later, cholera spread to the rest of Europe, and from Europe to North America and the rest of the world.

Seven cholera pandemics have happened in the past 200 years.  The latest started in Indonesia in 1961.  There have also been many serious outbreaks.  The worst outbreak in recent history happened in Haiti after the earthquake there in 2010.  Between October 2010 and August 2015, more than 700,000 Haitians got cholera, and over 9,000 died.  The outbreak was caused by a United Nations base where Nepalese soldiers were living.  The soldiers would dump human waste into the Artibonite River, which many Haitians used for drinking, cooking, and bathing.

Cholera was common in the 19th century. It has killed tens of millions of people.  Just in Russia, between 1847 and 1851, more than one million people died of cholera.  During the second pandemic, which lasted from 18271835, the disease killed 150,000 Americans.  Between 1900 and 1920, in India, up to eight million people died of cholera.

in 1854, an English doctor named John Snow was the first person to realize that contaminated water caused cholera. 

The English engineer Joseph Bazalgette solved the problem for London in the middle of the 19th century. He invented the system for cleaning foul water, a system which is still used world-wide. Cholera has come back to the world because cities have hugely increased populations, and the treatment of sewage has overrun the facilities. It was the British who built most of the world's sewage plants, and until about 1950 they were able to work well unless they were damaged by warfare. Later governments did not invest money in their infrastructure, which meant the increased population eventually caused cholera to return.

Cholera is not the only problem with water supply. Blooms of red algae occur from time to time in hot weather, and they have to be killed off. Emergency control is got by adding chlorine to the water supply. This works, but makes the water rather distasteful.

Fortunately, infections transmitted in bad water can be cured. There is at least one antibiotic which works well against amoeboid parasites, and another which usually works against bacteria. Treatment costs money, of course, and in many countries that means the treatment is not widely available.

References

Other websites 
 Information about cholera in Simple English from the CDC
 CDC facts about cholera
 WHO facts about cholera
 Rehydration Project talks about ORSs (oral rehydration solutions)

Diseases caused by bacteria
History of medicine