Cholera

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.

Prospects

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.

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