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.

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 diarrhoea 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.

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.