- Cholera is caused by the bacterium, Vibrio cholerae.
- It results in profuse watery diarrhoea.
- It is mostly contracted through eating or drinking contaminated food or water.
- Epidemics seem to follow a cyclical pattern.
- It can be fatal if left untreated.
Cholera is an acute illness that results in profuse watery diarrhoea. It's caused by a bacterium,Vibrio cholerae, an organism that lives in fresh water.
The World Health Organisation (WHO) estimates that there are 3-5 million cases of cholera annually with 100 000 - 130 000 deaths. In 2009, 221 226 cholera cases were reported to the WHO.
About 206 serotypes of cholera have been identified. Although many serotypes can cause cholera-like symptoms, only serogroups O1 and O139 are associated with widespread epidemics.
Under normal circumstances your gut absorbs water and nutrients from the food you eat and drink. When you are infected with the cholera, the bacterium releases a toxin that causes increased secretion of water and chloride ions from the intestine, which results in watery diarrhoea (up to 20 litres in a 70kg adult). If the diarrhoea goes untreated, death can result from severe dehydration and shock.
Most people contract cholera through drinking water or eating food that has been faecally contaminated by the bacteria. Person to person transmission is rare.
Uncooked shellfish, cooked rice, fresh fruits and vegetables can become sources of the disease, but potable water remains the most important source.
On the whole, cholera is a disease that affects economically disadvantaged communities with poor sanitary conditions. In developed countries such as the USA, cholera has been very rare over the last 100 years. Less than 10 cases are reported in the USA each year, mostly in travellers to endemic areas.
Epidemics usually occur in areas where there is loss of sanitary human waste disposal, lack of safe drinking water, and limited access to healthcare facilities usually in areas of 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, sub-Saharan Africa, Mexico, South and Central America.
Vibrio choleraeis a human pathogen. Epidemics seem to follow a cyclical pattern. Periods of rain are essential for a resurgence of the disease. When environmental conditions are unfavourable, the bacteria survive in the water by attaching to algae or the shells of shellfish. After heavy rains, however, when you have large quantities of fresh water at the mouth of rivers, the levels of salinity change and the organisms begin to multiply and move upstream. Communities living close to the river get infected when they use water from the river which is contaminated by the cholera bacteria.
As bacteria infect the community's water supply, more and more people become infected, until there's nobody else for the bacteria to infect, or the community has built up immunity.
Most recently, outbreaks have occurred in Haiti and Nigeria. The most recent outbreak in South Africa occurred in 2008-2009, when the cholera outbreak from Zimbabwe spread to several provinces, predominately Limpopo and Mpumalanga provinces.
The onset of cholera is usually sudden, with incubation periods ranging from one to five days.
Most people infected with cholera do not become ill. When illness does occur, about 80-90% have mild to moderate gastroenteritis. Less than 10% develop severe symptoms.
Cholera symptoms include:
- Diarrhoea (Look out for the characteristic "rice water" stools or diarrhoea that has a “fishy” odour.)
- Dehydration. Signs of dehydration include a rapid heart rate, dry skin, dry mucous membranes, extreme thirst, low blood pressure, lethargy, unusual sleepiness, infrequent urination, or sunken fontanelles in infants.
- Muscle cramps
Testing for cholera is done by taking a stool culture or rectal swab.
Although cholera can be life-threatening, it's easily prevented and treated. Successful treatment requires the replacement 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 must be given intravenously. With prompt rehydration, less than 1% of cholera patients die.
Although antibiotics may shorten the duration and severity of the symptoms, they're not as important as rehydration. Rehydration is the most important part of the treatment regime. For really ill patients, antibiotics that are known to be active against the infecting bacterium, such as tetracycline or ciprofloxacin may be administered.
Travellers to endemic areas who follow the usual tourist itinerary and observe the recommended safety precautions regarding safe drinking water and food have minimal risk of contracting cholera.
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. Most international organizations, such as the Centers for Disease Control (CDC) and the World Health Organisation, do not recommend cholera vaccination for travel.
During cholera epidemics, vaccination may be a short-term intervention, whilst long-term interventions such as provision of safe drinking water and sanitation are put into place.
Newer oral cholera vaccines have been developed that are more reliable than the injected form. These vaccines, however, don’t offer complete protection against the disease, and protection lasts about 2 years after immunisation. However, travellers to an endemic area with a significantly increased risk, such as relief/aid workers, or immunocompromised individuals may benefit from immunization, particularly if they are visiting rural areas.
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 viable in cholera areas.
Previously reviewed by Professor Willem Sturm, Head of the Medical Microbiology and Infectious Diseases department at the Nelson Mandela School of Medicine in Durban
Reviewed by Dr Miscka Moodley, Microbiologist, UCT, March 2011
1. Mandell, GL, Bennet, JE, Dolin, R. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th Edition. 2009: Churchill Livingstone.Vol 2, Chapter 214.
2. wwwnc.cdc.gov/travel/yellowbook/2010/chapter-5/cholera.aspx. Retrieved 15 March 2010.
3. www. who.int/topics/cholera/en/. Retrieved 15 March 2010.
4. National Institute of Communicable Diseases., NHLS. Communicable Diseases Communique. Jan 2009, Vol. 8, No. 1.
5. www.who.int/immunization/newsroom/news-revised_position/paper-cholera_vaccines/en/index.html. Retrieved 15 March 2010.
6. Waldor, MK, Hotez, PJ, Clemens, JD. A National Cholera Vaccine Stockpile- A New Humanitarian and Diplomatic Resource. NEJM. 2010(Dec 9). 363(24): 2279-2282.