Cholera is caused by the Vibrio cholerae bacterium
It results in profuse watery diarrhoea
It is mostly contracted through eating or drinking contaminated food or drink
Epidemics seem to follow a cyclical pattern
It can be fatal
What is cholera?
Cholera is an acute illness that results in profuse watery diarrhoea. It's caused by the Vibrio cholerae bacterium, a relatively simple organism that lives in fresh water. Cholera is a bacterial infection.
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Over the years160 strains of cholera have been identified. Of these strains, only two produce a toxin that causes diarrhoea. These are serogroups 01 and 0139. Simply put, the numbers help distinguish when the strains were identified. Vibrio cholerae 0139, for example, was only discovered about six years ago, while Vibrio cholerae 01 was the first strain to be identified many years ago.
Under normal circumstances, your gut absorbs water and nutrients from the food you eat and drink, but when you are infected with cholera, the opposite occurs. The toxin released by the bacteria causes increased secretion of water and chloride ions from the intestine, which results in watery diarrhoea. If the diarrhoea goes untreated, death can result from severe dehydration and shock.
What causes cholera?
Most people contract cholera through drinking water or eating food that has been fecally contaminated by the bacteria.
Uncooked shellfish, milk, cooked rice, lentils, potatoes, beans, eggs, chicken and coconut milk all can become sources of the disease, but potable water remains the most important source.
On the whole, cholera is a disease that preys on the disadvantaged because when piped water and sanitation is available, people usually do not get infected. In developed countries such as the USA, cholera has been very rare for the last 100 years. According to statistics, 0 – 5 cases are reported in the USA each year.
Developing countries don't escape so lightly, however. Epidemics usually occur in areas where there's poor sanitation, over-crowding, war or famine. But cholera can also spread after a natural disaster such as a flood or earthquake when fresh water supplies are disrupted.
Endemic areas include India, Asia, Africa, the Mediterranean, and more recently, South and Central America and Mexico.
Vibrio cholerae is a human pathogen and is dependent on people for survival. Epidemics seem to follow a cyclical pattern. Periods of rain are essential to a resurgence of the disease. When there is no outbreak, the bacteria are carried to the sea where in the river mouths the concentration of salt renders them dormant.
After heavy rains, however, when you have large quantities of fresh water at the mouth of the river, this upsets the levels of salinity and the organism begin to multiply and move upstream. If communities then drink the water, they can begin the process of re-infection once more. If they live in an impoverished community, they're unlikely to have proper sanitation and may use the local river for bathing and washing.
The bacteria then infects the community's water supply and so more and more people become infected, until there's nobody else for the bacteria to infect or the community has built up immunity.
Although outbreaks happen from time, the previous South African epidemic occurred in 1984 and predominantly affected people living in KwaZulu-Natal.
Symptoms of cholera
The onset of cholera is usually sudden, with incubation periods ranging from six hours to five days.
Cholera symptoms can range from mild to severe and include:
Diarrhoea (look out for the characteristic ‘rice water’ stools or diarrhoea that has a fishy odour);
Dehydration. Signs of dehydration include a rapid pulse, dry skin, dry mucous membranes, extreme thirst, lethargy, unusual sleepiness, infrequent urination or sunken fontanelles in infants;
Abdominal cramps;
Nausea;
Vomiting;
Testing for cholera is done by taking a stool culture. (cholera does not get into blood).
How is cholera treated?
Although cholera can be life-threatening, it's easily prevented and treated. Successful treatment requires the replacing of fluids and salts lost through diarrhoea.
Depending on the condition of the patient, a pre-packed mixture of sugar and salts can be mixed with water and drunk in large quantities.
If the patient is too weak to drink, fluids can be given intravenously. With prompt rehydration, fewer than 1% of cholera patients die.
Although antibiotics may shorten the duration of the symptoms, they're not as important as rehydration. Rehydration is the most important part of the treatment regime. For really ill patients, tetracycline used to be the drug of choice, but the South African bacteria are resistant to this antibiotic. Therefore, the recommended drug is ciprofloxacin (Ciprobay from Bayer Pharmaceuticals).
Can cholera be prevented?
Although there is a vaccine for cholera, it offers only limited immunity and the jury is out about whether or not travellers should be vaccinated.
While some doctors recommend it, others doubt its efficacy and suggest that travellers should rather take precautions with food and drinking water.
During cholera epidemics, vaccination is not effective and the best way to tackle the disease is to educate the community on how to make water and food safe and sanitation, or to provide clean water.
A new, oral cholera vaccine has also been developed that is more reliable than the injected form, but it's expensive and doesn't offer complete protection against the disease.
Regretfully, none of the current vaccines have the necessary combination of high efficacy, long duration of protection, simplicity of administration and low cost to make mass vaccination a possibility in cholera areas.
Reviewed by Professor Willem Sturm, Head of the Medical Microbiology and Infectious Diseases department at the Nelson Mandela School of Medicine in Durban.
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