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'Cholera is not really a tropical disease, but is related to standards of hygiene and the quality of drinking water. It was a single well in London in the 1850-60s that was the source of several separate cholera epidemics.

John Snow is regarded as a father of public health by his simple but brilliant removal of the handle to the Broad Street water pump!'

John Snow and Cholera

Map Stops Cholera: John Snow's Map of London
The Broad Street Cholera Outbreak of 1854
Dr John Snow named the greatest doctor ever
Mugabe: 'There is no cholera in Zimbabwe'
Zimbabwe cholera: A plague of Robert Mugabe's own making
Crisis Mounts As Harare Water System Shut Down
What is Cholera?
See also

John Snow (15 March 1813 – 16 June 1858) was a British physician and a leader in the adoption of anaesthesia and medical hygiene. He is considered to be one of the fathers of epidemiology, because of his work in tracing the source of a cholera outbreak in Soho, England, in 1854.John Snow (15 March 1813 – 16 June 1858) was a British physician and a leader in the adoption of anaesthesia and medical hygiene. He is considered to be one of the fathers of epidemiology, because of his work in tracing the source of a cholera outbreak in Soho, England, in 1854.

Snow was a skeptic of the then-dominant miasma theory that stated that diseases such as cholera or the Black Death were caused by pollution or a noxious form of "bad air". The germ theory was not widely accepted at this time, so he was unaware of the mechanism by which the disease was transmitted, but evidence led him to believe that it was not due to breathing foul air. He first publicized his theory in an essay On the Mode of Communication of Cholera in 1849. In 1855 a second edition was published, with a much more elaborate investigation of the effect of the water-supply in the Soho, London epidemic of 1854.

By talking to local residents (with the help of Reverend Henry Whitehead), he identified the source of the outbreak as the public water pump on Broad Street (now Broadwick Street). Although Snow's chemical and microscope examination of a sample of the Broad Street pump water was not able to conclusively prove its danger, his studies of the pattern of the disease were convincing enough to persuade the local council to disable the well pump by removing its handle. Although this action has been commonally reported as ending the outbreak, the epidemic may have already been in rapid decline, as explained by Snow himself:

There is no doubt that the mortality was much diminished, as I said before, by the flight of the population, which commenced soon after the outbreak; but the attacks had so far diminished before the use of the water was stopped, that it is impossible to decide whether the well still contained the cholera poison in an active state, or whether, from some cause, the water had become free from it.

Snow later used a spot map to illustrate how cases of cholera were centred around the pump. He also made a solid use of statistics to illustrate the connection between the quality of the source of water and cholera cases. He showed that companies taking water from sewage-polluted sections of the Thames delivered water to homes with an increased incidence of cholera. Snow's study was a major event in the history of public health, and can be regarded as the founding event of the science of epidemiology.

In Snow's own words:

On proceeding to the spot, I found that nearly all the deaths had taken place within a short distance of the [Broad Street] pump. There were only ten deaths in houses situated decidedly nearer to another street-pump. In five of these cases the families of the deceased persons informed me that they always sent to the pump in Broad Street, as they preferred the water to that of the pumps which were nearer. In three other cases, the deceased were children who went to school near the pump in Broad Street...

With regard to the deaths occurring in the locality belonging to the pump, there were 61 instances in which I was informed that the deceased persons used to drink the pump water from Broad Street, either constantly or occasionally...

The result of the inquiry, then, is, that there has been no particular outbreak or prevalence of cholera in this part of London except among the persons who were in the habit of drinking the water of the above-mentioned pump well.

I had an interview with the Board of Guardians of St James's parish, on the evening of the 7th inst [Sept 7], and represented the above circumstances to them. In consequence of what I said, the handle of the pump was removed on the following day.

—John Snow, letter to the editor of the Medical Times and Gazette

It was discovered later that this public well had been dug only three feet from an old cesspit that had begun to leak fecal bacteria. A baby who had contracted cholera from another source had its nappies washed into this cesspit, the opening of which was under a nearby house that had been rebuilt farther away after a fire had destroyed the previous structure, and the street was widened by the city. It was common at the time to have a cesspit under most homes. Most families tried to have their raw sewage collected and dumped in the Thames to prevent their cesspit from filling faster than the sewage could decompose into the soil.

Political controversy
After the cholera epidemic had subsided, government officials replaced the Broad Street Handle Pump. They had responded only to the urgent threat posed to the population, and afterwards they rejected Snow's theory. To accept his proposal would be indirectly accepting the oral-fecal method transmission of disease, which was too unpleasant for most of the public.

Public health officials today recognize the political struggles that reformers often get entangled in. During the Annual Pumphandle Lecture in England, members of the John Snow Society remove and then replace a pump handle to symbolize the continuing challenges that face public health advancements.

Later life
Snow was a vegetarian and an ardent teetotaler and believed in drinking pure water (via boiling) throughout his adult life. He never married.

At the age of 45, Snow suffered a stroke while working in his London office on 10 June 1858. He never recovered, dying on 16 June 1858 and is buried in Brompton Cemetery.


Map Stops Cholera: John Snow's Map of London
By Matt Rosenberg,

In the mid-1850s, there were two major theories about the transmission of cholera. Dr. John Snow used techniques which would later be known as medical geography to confirm that the transmission of the disease occurred by swallowing contaminated water or food and not by inhaling infected air.

John Snow's map depicts the proximity of cholera cases to public water pumps

Dr. Snow knew that he had identified the transmission method for the "cholera poison." This "poison" was later identified as the bacterium VIBRIO CHOLERAE. Cholera leads to an infection of the small intestine which results in extreme diarrhea which may lead to massive dehydration and death. The disease can be treated by giving the victim a lot of fluids -- either by mouth or intravenously (directly into the blood stream).

As sanitation and more effective water treatment increases throughout the world, the number of cholera victims decreases. Cholera has existed in Northern India for centuries and it is from this region that regular outbreaks are spread. The disease diffuses as people travel from the source area. With modern transportation such as airplanes, diseases can be spread a great distance very rapidly.

In the nineteenth century, there were several outbreaks of cholera in London. In the 1849 outbreak, a large proportion of the victims received their water from two water companies. Both of these water companies had the source of their water on the Thames River, just downstream from a sewer outlet. In an 1854 outbreak, most of the deaths occurred within the area of the Southwark and Vauxhall Water Company. Fortunately, just before the outbreak, the Lambeth Water Company relocated their water source to a less polluted point so fewer deaths occurred among their customers. The distribution of deaths was one of the primary factors which proved that the deaths were caused by ingestion.

Dr. Snow plotted the distribution of deaths in London on a map. He determined that an unusually high number of deaths were taking place near a water pump on Broad Street. Snow's findings led him to petition the local authorities to remove the pump's handle. This was done and the number of cholera deaths was dramatically reduced.

The work of Doctor Snow stands out as one of the most famous and earliest cases of geography and maps being utilized to understand the spread of a disease. Today, specially trained medical geographers and medical practitioners routinely use mapping and advanced technology to understand the diffusion and spread of diseases such as AIDS and cancer. A map is not just an effective tool for finding the right place, it can also be a life saver.


John Snow and the Broad Street Cholera Outbreak of 1854

Cholera reached the British Isles in the early 1830s, and outbreaks would continue for the next fifty years. Today, it is well known that cholera is caused by the bacteria Vibria cholerae and is usually spread in poor drinking water. Early theories blamed the infection on mists and 'miasmas', which led to many of the early attempts to control cholera failing. In reality the poor sanitary conditions of a city's water supply was responsible. Early Victorian cities also included cowsheds mixed in amongst the houses. These combined with poor handling of human sewage (often merely a hole in the ground) led to a rapid contamination of the drinking water. Indeed, the famous Broad Street water pump (see below) was a shallow water pump that pumped water from the contaminated water table.

In the 1850s, John Snow performed pioneering data analysis to prove his hypothesis that cholera was spread in the drinking water. This analysis if performed today, would come under the realms of GIS (Geographic Information Systems) and Data Mining. Some have claimed his Broad Street map as being the first example of GIS, even though it was performed with a pen and paper. Although this is an exaggeration, the Broad Street map it is an excellent example of the power of maps to clearly demonstrate relationships in complex scenarios. Snow's work with the London cholera outbreaks of the 1850s, is often cited as the beginning of modern epidemiology.

Unfortunately word of this pioneering epidemiology was slow to spread, and the London cholera outbreaks would continue into the 1880s when all of the shallow water-pumps were finally decommissioned.

This page looks at Snow's two most famous analysis cases that helped to prove his hypothesis that cholera infections occurred through drinking water.

The Broad Street Outbreak, 1854

This is the most famous piece of data analysis performed by John Snow, and his prompt action undoubtedly saved many lives. The outbreak occurred in the Soho District of London, in and around Broad Street.

John Snow reasoned that if cholera was spread by a mist or miasma, as the prevailing theories suggested, then the cases should be uniformly distributed along the streets. To see if this was the case, he plotted each cholera case on a map, similar to the one on the left. He also plotted houses with multiple cases, which the modern map on the left does not show.

As can be seen, the cases are not uniformly distributed, but instead are distributed in a tight cluster around a water pump located on Broad Street (now Broadwick Street). Snow went to the pump and took a water sample. Looking in his microscope, he found the water contained a bacteria which he had not seen before. Although he guessed these were responsible, this was before the infectious microbe work of Pasteur and Koch.

He went back to the pump and removed the pump handle. The Broad Street cholera outbreak stopped almost literally overnight.

Not noted on the map was some other evidence which helped to support the water pump hypothesis. A local workhouse was almost untouched (only five cases), due to it using water from its own uncontaminated well. The map also shows some outliers. Snow's investigations showed that these were due to people who would pass the well (eg. on the way to work) and take drink.

The Grand Experiment, 1853-54
Although John Snow is most famous for his analysis of the Broad Street outbreak, this analysis merely confirmed a theory he had been developing over the preceding years. One of his biggest tests was what he called his "Grand Experiment", and was carried out throughout the outbreak of 1853-54. He carefully analysed the cholera deaths in London, correlating them with the source of drinking water.

As well as hand pumps such as at Broad Street, much of London's population received machine-pumped water similar to what we have today but without the treatment plants. Two companies supplied water like this. Due to new laws, the Lambeth Company had started to take its water from the River Thames about 20 miles up-stream of London, but the Southwark and Vauxhall Water Company was still taking its water from local wells and the Thames in Central London. This provided a perfect comparison for Snow.

Snow's final summary table:
Cholera deaths
Deaths per 10,000 houses
Southwark & Vauxhall Company
Lambeth Company
Rest of London

Hence, Snow showed a strong correlation between the cholera death rate and the water source. The data also shows that a water source up-river of the London was the safest option, whilst taking water directly from the Thames in Central London was more dangerous than other local water sources combined.

Cholera, Chloroform and the Science of Medicine: A Life of John Snow by Peter Vinten-Johansen et al is a comprehensive biography of John Snow based on six years of research. 

The World Health Organisation have a Cholera Fact Sheet, including details about the current pandemic.

The John Snow Society aims to promote the life and works of Dr. John Snow.

UCLA's School of Public Health has a very comprehensive website devoted to John Snow.


Dr John Snow named the greatest doctor

Hospital Doctor, March 2003

Dr John Snow has been voted the greatest doctor ever in a Hospital Doctor poll.

Readers were invited to consider a number of doctors worthy of the title, but it was the nomination of Dr Snow by Dr Guy Jackson, a research fellow in anaesthesia in London, that attracted the most support. He was backed by an active campaign from the John Snow Society.

Dr Snow (1813-1858), a GP based in Soho, developed the technique of anaesthesia.

According to Dr Jackson, Dr Snow's book On The Inhalation Of The Ether Vapours 'was the definitive work of its day, using scientific principles and practice more akin to those used today than those used by his contemporaries'.

He was called on by Queen Victoria to provide analgesia for childbirth. She described his care as 'most efficacious'.

Dr Snow also developed drugs including chloroform, theories on the transmission of cholera, and was seen as one of the founders of intensive care medicine.

In second place was Hippocrates (460-370BC), who taught that illness was not down to the influence of evil spirits and that doctors could help through evidence-based medicine. He wrote more than 70 books and introduced the oath.

Dame Cicely Saunders (1918-), founder of the modern hospice movement, came third.

Mugabe: 'There is no cholera in Zimbabwe'
He's not unhinged, but he is ridiculous:
Richard Beeston's analysis. December 11, 2008

President Robert Mugabe said today that “there is no cholera” in Zimbabwe any more because the country's doctors had cured the outbreak.

His statement is in stark contradiction of the daily updates on the state of Zimbabwe's cholera epidemic from the World Health Organisation, which said today that at least 783 had died of the disease and 16,403 had been infected as of yesterday.

Today South Africa declared its border with Zimbabwe a disaster zone because of the surge of people trying to cross the border, either fleeing the disease or seeking medical treatment, as Zimbabwe's economy and health care system has largely collapsed.

“I am happy to say our doctors have been assisted by others and WHO (the World Health Organization)... so now that there is no cholera,” said Mr Mugabe, in a speech screened on national television.

The veteran President, who has led Zimbabwe ever since independence from British colonial rule 28 years ago, linked international concern at Zimbabwe's plight to what he regarded as a plot to oust him from power.

He denounced calls by Gordon Brown, Nicolas Sarkozy of France and President Bush for him to step down.

“Because of cholera, Mr Brown, Mr Sarkozy and Mr Bush want military intervention. Now that there is no cholera, there is no need for war,” he said.

“The cholera cause doesn’t exist any more.

“Shall we also say that (because) there is mad cow disease, there must be war, Britain must be invaded? Mr Brown, your head must go for some medical correction."

Meanwhile a spokesman for the Limpopo provincial government in northern South Africa revealed today that the area had been accorded disaster status at an emergency meeting this week.

“The whole of the Vhembe district has been declared a disaster,” said Mogale Nchabeleng. “Extraordinary measures are needed to deal with the situation."

Cholera has also been reported spreading into neighbouring Mozambique, Zambia and Botswana.

The outbreak has prompted calls from Britain, France and the US for international humanitarian assistance to be sent into Zimbabwe. Western leaders and some African leaders have also called on Mr Mugabe to resign.

Zimbabwean government spokesmen have repeatedly accused the West of using the cholera epidemic - the worst in Zimbabwe's history - to try to oust Mr Mugabe. They also blame Western sanctions for ruining the once relatively prosperous southern African country, where inflation is so high that prices double every 1.3 days.

Mr Mugabe’s critics say it is his policies which have wrecked the Zimbabwean economy and led to the deaths of thousands of his people. Half the population is dependent on foreign food aid in a country that until recently exported food to its neighbours.

Mr Mugabe remains deadlocked with Morgan Tsvangirai, the opposition leader, over implementing a power-sharing deal.

South Africa’s ruling African National Congress said today that it was unnecessary to intervene in Zimbabwe as it believed that 84-year-old Mr Mugabe could be persuaded to retire.

“I don’t think invading Zimbabwe or sanctions would work," Gwede Mantashe, the ANC secretary general, told the SAPA news agency.

“What will we do to make Mugabe retire? We will persuade him.”


Zimbabwe cholera: A plague of Robert Mugabe's own making
By Peta Thornycroft and Sebastien Berger 6 Dec 2008

Zimbabwe's cholera epidemic is a deadly symptom of the corruption of the country's rulers.

When cholera first began rampaging through Zimbabwe's impoverished towns and cities, Robert Mugabe's government tried to play down the epidemic. According to official figures, it has now killed almost 600 people, and this week, the authorities finally gave in and appealed for international help. Health minister David Parirenyatwa admitted: "Our central hospitals are literally not functioning."

But openness is not the norm for officials in Harare, Zimbabwe's capital. At the Budiriro Polyclinic, in the high-density western suburbs, the fence has been covered in plastic sheeting to stop people seeing in. Outside the barrier, more than 50 relatives wait anxiously for news of their loved ones.

Inside, one Zimbabwean doctor and several foreigners plunge multiple drips into cholera victims, whose bodies have been emaciated by hunger and dehydrated by the horrendous diarrhoea that is main symptom of this.

The clinic's capacity has been trebled in the past fortnight, to almost 300 patients a day. Next to the building, a green tent has been set up in which bare light bulbs hang over rows of stretchers, and Unicef have an outpost packed with drips, drugs and medical paraphernalia. But it is not enough.

"No matter how much medicine they bring, they are not going to contain this cholera, because they are treating the symptoms rather than the disease," says Tongesai, a well-educated man in his mid-30s whose younger brother was admitted earlier in the day. "The cholera is coming from the water, which is contaminated. It is not the boreholes that are bringing in the contaminated water, but the water from the city. That water is now getting to the people without being treated, and that is how people get cholera. It is tantamount to drinking raw sewage." And this is why Mugabe's government bears ultimate responsibility for the suffering of its people.

By a cruel irony, the name of the suburb – Budiriro – means "progressing" in Zimbabwe's majority Shona language. For several years after independence in 1980, it lived up to its name. Mugabe inherited a fine health service, despite the bush war that had cut off large parts of the countryside. Preventive health care expanded enormously as exiled black doctors flocked home, foreign donors gave generously and the economy grew.

That came to an end in 2000, when Mugabe started seizing white-owned farms, ostensibly on behalf of landless blacks but in reality to hand them out to cronies to shore up support within the ruling Zanu-PF party. The move destroyed commercial agriculture, the source of most of the country's export earnings, and precipitated the collapse of the economy. As the government's own income fell in tandem, it started printing ever more bank notes to meet its own needs. The result was a vicious circle of hyperinflation, and a government utterly incapable of maintaining Zimbabwe's infrastructure.

In Budiriro – now a stronghold of the opposition Movement for Democratic Change – and elsewhere there are hardly any teachers left. Health workers have left for South Africa, Britain or Australia, or simply downed syringes because of their insultingly low pay, which they cannot in any case retrieve from their bank accounts. Under many roads in the township, the clay sewage pipes have crumbled, so that even in the searing heat of an unusually dry early December, pools of stinking water fester while children play nearby.

The town of Beitbridge, on the border with South Africa, has been almost as badly hit by the epidemic as Harare – and offers another graphic demonstration of the government's culpability. There, cholera spread as a result of houses built by the authorities after Mr Mugabe's "Murambatsvina" or "Clean out the trash" campaign of 2005, in which hundreds of thousands of poor urban residents, mostly MDC supporters, lost their homes.

"The government built these [new] houses on the upper part of the town, but put in no water or sewage systems," explains a health worker. "People are using the bush, and when the rain came last month it brought their faeces into the Limpopo River and into the town's water supply. That is how it started."

The only ones who might profit from this are the undertakers, but even they aren't seeing an upturn. "We don't get any cholera bodies," says Edward, the manager of the White Dove funeral parlour in Budiriro, "as they have to go to the City of Harare or the Ministry of Health. So there is no extra business for us." But he is still busy: yesterday there were about 10 bodies, mostly younger people, in the cold room. The cholera outbreak comes on top of an Aids epidemic that has left Zimbabwe with one of the lowest life expectancies in the world.

Even Mr Mugabe's machinery of repression is creaking under the strain. Groups of uniformed soldiers have rioted several times in Harare in recent days, out of frustration at their inability to withdraw their wages. But the protests were quickly crushed by riot police; several soldiers have been arrested, and sources say that others have been humiliated by senior officers back in their barracks.

Still, no one expects a coup or popular revolution any time soon. The civilians have been crushed by years of brutality, and are fully occupied merely trying to survive. The disgruntled soldiers are low-ranking and disorganised, whereas the reliability of the riot police is ensured by extra pay and privileges. The upper echelons of the military are loyal members of the Zanu-PF network, with their own interests to protect – not least the risk of prosecution for gross violations of human rights under any new government.

Zanu-PF is also so factionalised that Mr Mugabe remains essential to keeping it together. By playing off different groupings, and refusing to create a succession plan, he has ensured that his chieftains would rather keep him in office than see their rivals take the presidency.

Under a power-sharing agreement, MDC leader Morgan Tsvangirai is due to become prime minister, but a constitutional amendment is needed that will not be in place until the early part of next year, and could still be delayed further. The deal will give Mr Tsvangirai a veto over senior government appointments, among other powers, but it is certain that Mr Mugabe, whose bad faith was demonstrated by his unilateral allocation of government ministries between the parties, will do his utmost to maintain his control.

In the meantime, the suffering of Zimbabwe's people continues – and worsens. The Infectious Diseases Hospital, about five miles south of Harare on the pockmarked highway to South Africa, is the only government hospital still open in the capital. Between five and 15 cholera fatalities arrive at its mortuary every day.

Outside the building, one of the lucky ones, Regina Chifamba, sits on a bench, crying. The 28-year-old, whose frailty belies her age, has just been released after being successfully treated for cholera. But she has no idea what has happened to her 12-year-old son, Blessing.

While in hospital she was told he too had been admitted, but his name did not appear in the records, so she has no way of knowing whether he has been discharged, disappeared, or died.

"We don't know what our political leaders have thought of us," she says. "They are busy buying fuel and cars for the ministers, but spend nothing to treat our water. Now I can't even find my son."


Zimbabwe Cholera Crisis Mounts As Harare Water System Shut Down
By Peta Thornycroft, Patience Rusere, James Butty & Irwin Chifera. 1 December 2008

Zimbabwe appeared Monday to be spiraling into a complex humanitarian emergency with cholera spreading nationwide with the death toll mounting into the hundreds, the public water system in Harare shut off for fear of contaminated water spreading cholera even further, and soldiers rioting in the capital over restrictions on cash withdrawals from banks.

"The country is reaching a catastrophic level in terms of food, health deliver, education," said Morgan Tsvangirai, founder of the Movement for Democratic Change and slated to become prime minister in the proposed unity government in the works since Sept. 15. "Everything seems to be collapsing around us," AFP reported Tsvangirai as saying.

The state-controlled Herald newspaper said the Zimbabwe National Water Authority cut off water to Harare because it ran out of a chemical needed to purify drinking water.

The rainy season is now upon Zimbabwe and authorities fear that human feces deposited in open spaces along the Mukuvisi River will be carried into the public water supply, potentially contaminating it with the bacteria that causes cholera, infecting thousands more.

Medical sources estimate that as many as 10,000 people have contracted the disease and the death toll, set by Harare at 425 on the weekend, is believed to be much higher as it is thought that many deaths have occurred in homes and not been recorded.

Elsewhere, the British humanitarian organization Save The Children said two children and one adult in the Zambezi valley had died of anthrax. It said people are so hungry they are eating the meat of dead animals though such meat is probably infected with the disease.

Anthrax usually only afflicts animals, but can be transmitted to humans who handle or eat the meat of the infected animals. The group said 60,000 head of livestock were at risk.

Harare has asked for international aid while blaming the crisis on Western targeted sanctions.

Meanwhile, eyewitnesses told VOA that police and soldiers fought running battles in Harare's city center after the troops ran amok in a repitition of disturbances Friday. The solders were said to be angered over their inability to withdraw more than Z$500,000 from their bank accounts, a sum which is barely enough for bus fare into Harare and home.

VOA's Peta Thornycroft reported on one of the victims of the cholera epidemic, a civil rights activist who previously had survived many arrests on the streets of Harare.

For an update on the cholera epidemic, reporter Patience Rusere of VOA's Studio 7 for Zimbabwe turned to Dr. Douglas Gwatidzo, chairman of the Zimbabwe Association of Doctors for Human Rights, who said the official estimate of 425 deaths is too optimistic.

VOA reporter James Butty spoke with Health Minister David Parirenyatwa, who said that the country’s political and economic crisis must be resolved to address the health crisis.

The attention of many Zimbabweans was turned to the cholera crisis rather than World AIDS Day though observances were held in Bindura, Mashonaland West province.

President Robert Mugabe addressed the nation on the subject of HIV/AIDS Sunday evening in a pre-recorded address, and Dr. Henry Madzorera, health secretary of the MDC grouping led by Tsvangirai, responded, as correspondent Irwin Chifera reported.


Written by Dr Charlie Easmon, specialist adviser in travel medicine
What is cholera
Cholera is an infectious disease caused by a bacterium that affects the absorption of water in the small intestine.

In severe cases it produces violent diarrhoea within only a few days. The dangerous aspect of cholera is the vast loss of fluid that can occur in a short space of time. It is particularly dangerous in children in developing countries.

If untreated, the loss of fluid can be fatal within 24 hours of developing the disease. On the other hand, treatment is simple: replace the fluid with the right mix of sugar and salts - water alone is not adequately absorbed.

However, bad cases do require admission to hospital where fluids can be administered straight into the bloodstream via a drip.

Cholera is not really a tropical disease, but is related to standards of hygiene and the quality of drinking water. It was a single well in London in the 1850-60s that was the source of several separate cholera epidemics.

John Snow is regarded as a father of public health by his simple but brilliant removal of the handle to the Broad Street water pump!

Improved sanitation and hygiene are still the basic foundation of the fight against cholera in those countries where it occurs.

What causes cholera?
Cholera is caused by a specific bacterium, Vibrio cholerae.

When an adequate quantity of the bacteria has passed into the stomach in food they accumulate and begin to produce poisonous substances (toxins). It is the toxin that causes the symptoms of the disease.

The cholera toxin has the unpleasant ability to affect the cells of the gastrointestinal tract so that the affected person doesn't just get ordinary diarrhoea, but also starts to lose very large quantities of fluid. It is this fluid loss that can be very serious.

How is cholera transmitted?
Bacteria are excreted in faeces and if this comes into contact with drinking water, the bacteria can infect people. Bacteria can also spread to food if people don't wash their hands thoroughly after using the toilet. The food prepared at the funeral of a cholera victim is a common source of secondary spread in Africa!

The disease can be spread through fish and shellfish from contaminated water. Shellfish filter large quantities of water and concentrate the bacteria. The cholera outbreak in Peru in 1998 was thought to be related to contaminated algae and it appears that this is a very effective way for cholera to spread to coastlines.

Direct infection by contact with another person via their faeces or vomit may occur, but is unusual. A certain amount of bacteria is needed before people with normal quantities of stomach acid become ill (stomach acid is able to kill small quantities of bacteria). So the bacteria need an opportunity to multiply in water or food before it actually constitutes a risk.

Where does cholera occur?
Cholera is very common in Asia and Africa, where epidemics occur at regular intervals. Unfortunately, the 'El Tor' cholera bacterium found its way to parts of Peru in the 1990s, and from there, spread rapidly throughout the remainder of the South America.

Densely populated, poor areas with little sanitation and unsatisfactory food hygiene are particularly affected by epidemics.

What are the symptoms of the disease?
The incubation period, from infection until the disease breaks out, is generally less than two days, although it can be as long as five days. The infection is often a mild illness with ordinary diarrhoea, and it can even evolve without any symptoms at all. But the individual is still able to pass on the disease.

Typically, cholera begins over quite a short period of time with stomach pains without feeling sick. There may also be a mild fever. Then vomiting and diarrhoea begins, and may continue for several hours.

This is followed by very copious, watery diarrhoea, which is pale and flaky and looks like rice water. The fluid loss may be as high as 1 litre every hour.

Danger signals
If the fluid loss is not replaced and exceeds 5-10 litres, it can be fatal.

Extensive dehydration can produce floppy skin, muscle cramps and a hoarse voice. There is also an effect on the level of consciousness, and this may manifest itself as lethargy and confusion. The electrolyte (salt) balance may also be disturbed and in children particularly this can cause convulsions or cardiac arrest.

Mild cases of cholera usually recover on their own.

Classic cholera has a high mortality rate if it is not treated. In developing countries, mortality among those admitted to hospital without treatment is 60 per cent.

If the illness is treated quickly and properly, the mortality rate is below 1 per cent and the patient recovers completely.

How can you avoid infection?

• Only drink boiled water or water that has been sterilised or treated in another way. Hot coffee and tea, fizzy water and other uncontaminated bottled drinks are usually safe enough to drink.

• Boil unpasteurised milk before you drink it.

• Avoid ice cubes in drinks, unless you can be sure they were made from 'safe water'! Ice cream from doubtful sources may also be contaminated.

• Food must be properly prepared and still hot when it is served. If it is allowed to stand at room temperature for several hours other bacteria such as Escherichia coli may develop.

• Avoid raw fish and shellfish.

• Avoid raw fruit and vegetables, unless you peel it yourself.

• Be careful eating food from street stalls. If you have to eat this type of food, think carefully about its preparation. Make sure it doesn't contain anything that hasn't been properly prepared.

This advice will protect you, not just against cholera, but also against a whole range of bacteria that can cause unpleasant diarrhoea. Some bacteria, however, produce toxins that are not destroyed by boiling. This is why correct food storage is also important.

Vaccination against cholera is now possible with the oral vaccine Dukoral. However, this vaccine does not provide 100 per cent protection against the disease and people who have had the vaccine will still need to follow the measures outlined above to avoid illness. This vaccine is most likely to be suitable for backpackers and those travelling to situations where the risk of cholera is greatest (eg refugee camps).

If you think you have caught cholera on a trip
If you think you have caught cholera you should see a doctor immediately. But do not despair if you are miles away from a hospital or doctor.

The most important thing you can do yourself in any case of violent diarrhoea is to consume large quantities of fluid with salt and sugar (alternatives include flat cola drinks), even if you are vomiting in between. There are powders with salt, bicarbonate and sugar in the correct ratio mixture that can be dissolved in water and taken, such as Dioralyte, WHO Rehydration satchets or Rehidrat.

You can also produce this fluid yourself from the following ingredients. The liquid should be about as salty as tears.

1 litre of boiled water.
8 level or 4 heaped teaspoons of sugar (white, brown or honey).
1/2 teaspoon of salt.
The juice of a lemon or orange.

How is the disease diagnosed?
Many diseases cause diarrhoea, but if it is violent with watery stools, the doctor will treat you immediately. To make a definite diagnosis, the stools have to be examined to detect the cholera bacteria.

How is cholera treated?
Severe cases of the disease must be treated in hospital.

The first and most vital measure is to replace the fluid lost. If speed is important, fluid may be administered directly into the bloodstream by a drip.

During epidemics, 90 per cent of those who get ill would be okay if they drank large amounts of water.

The course of the disease can be shortened and the excretion of bacteria stopped quicker by giving antibiotics, such as doxycycline (eg Vibramycin).

See also
Zimbabwe - No land changes: Govt
London: The Great Stink 
China's new slave empire
A long way from Gorky Park 1862 outbreak
Glasgow the City 1832 outbreak

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