Cholera is caused by infection with the bacterium Vibrio cholerae. Vibrios are one of the most common organisms in surface waters of the world. Although the reservoir has always been assumed to be humans, there is some evidence of an aquatic reservoir.
It can produce watery diarrhoea that is very profuse and this can rapidly lead to severe dehydration and death. Transmission is usually from contaminated water and direct person-to-person transmission by the faeco-oral route can occur.
Over 100 serotypes of V. cholerae exist but only two cause disease. V. cholerae O1 has two variants called classical and El Tor. The other pathogen is O139.
There are other types of species of V. cholerae which also cause infection in humans. They include V. parahaemolyticus, V. mimicus, V. damsela and V. hollisae and they also cause diarrhoea. There are also two other related families called aeromonas and plesiomonas and they cause diarrhoea, wound infections, septicaemia, ocular infections and meningitis.
Two serotypes of V. cholerae cause epidemic cholera (serotype O1 and serotype O139). Serotype O1 is further divided into classical and El Tor biotypes. The World Health Organization (WHO) reports the emergence of new, apparently more virulent, strains of V. cholerae O1 which now predominate in parts of Africa and Asia, and the emergence and spread of antibiotic-resistant strains.
- The disease is not endemic to the United Kingdom and is rarely imported from abroad (an average of only 10 cases of cholera are imported into the UK annually). The most common serotype is V. cholerae El Tor and most infections are acquired on the Indian subcontinent.
- The disease is endemic to parts of Africa, Asia, the Middle East and South America. Large outbreaks are common after natural disasters or in populations displaced by war, where there are inadequate sewage disposal and contaminated water.
- The cholera burden has grown strikingly during a period of four years, and has spread to countries previously spared by this disease.
- Most of the recent pandemics have been due to El Tor but O1 classical and O139 are endemic in India and Bangladesh.
- Non-O1 and non-O139 V. cholerae can cause mild diarrhoea but do not generate epidemics.
- There are an estimated 3-5 million cholera cases and 100,000-120,000 deaths due to cholera every year.
Risks for travellers
- The risk of cholera for most travellers to endemic areas is very low. The overall incidence of cholera in travellers is only 2-3 per million but, for those staying in areas of outbreaks, the incidence rises to 5 per thousand.
- Short-term travel has an extremely low risk and is in the order of 2 or 3 cases per million travellers.
- A high infecting dose (as many as 1,011 organisms) is necessary to cause illness in healthy individuals.
- Drinking untreated water or eating poorly cooked seafood in endemic areas carries a high risk.
- Travellers living in unsanitary conditions, such as humanitarian relief workers in disaster areas, are also at risk.
The majority (around 75%) of people who are infected with cholera do not become ill, although they can be excreting the organism for 7 to 14 days.
A number develop a moderate form of diarrhoea that is clinically indistinguishable from other forms of gastroenteritis. No more than 10% develop the very profuse diarrhoea that is regarded as characteristic of the disease.
- The incubation period is usually 2-5 days, although it can be a few days.
- Severe illness - sudden onset of profuse, watery diarrhoea with nausea and vomiting.
- The volume of fluid lost can be up to 20 litres a day.
- If not replaced, heavy fluid loss rapidly leads to serious dehydration and circulatory collapse.
- Untreated, around 50% of severe cases will die within a few hours of onset.
The severely dehydrated patient will look very unwell with sunken eyes and possibly impaired level of consciousness. Skin will be dry and lacking turgor. Pulse will be fast but weak with a low blood pressure indicating haemodynamic instability.
- Stool specimen to identify the organism.
- U&E, as the patient is likely to be significantly dehydrated, and to monitor IV fluid replacement. Creatinine may rise if the kidneys fail with circulatory collapse.
- FBC will often show a high Hb with haemoconcentration.
- WCC is likely to be raised but will not aid diagnosis or management.
A good way of estimating net fluid loss or gain if changes are large is to weigh the patient daily. 1 kg of weight represents 1 litre of fluid.
Cholera is an easily treatable disease. Prompt correct treatment reduces mortality to less than 1%.
- The basis of treatment is the replacement of lost fluid.
- This may be done orally if not very severe or if there is no access to facilities for IV replacement but the latter is required in severe fluid loss.
- Up to 80% of people can be treated successfully through prompt administration of oral rehydration salts.
- Antibiotics should be considered in severe cases of dehydration. Tetracycline, doxycycline or ciprofloxacin are often used. They reduce the rate of stool output and this shortens the duration of hospital stay, stops excretion of vibrio in the stool and minimises the requirement of fluids.
- Mass administration of antibiotics is not recommended, as it has no effect on the spread of cholera and contributes to increasing antimicrobial resistance.
- Resistance to many of these drugs has been observed and is a matter of concern.
Antidiarrhoeal and antisecretory drugs
- Antidiarrhoeal drugs are not recommended.
- Many antisecretory drugs have been tried as an adjunct therapy but none has been found useful.
All travellers should take sensible precautions about food and water hygiene. An oral cholera vaccine is now available in the UK - see separate article Cholera Vaccination for more details. The vaccine is not required by most travellers but may be suitable for those who are unable to take adequate precautions in highly endemic or epidemic settings. This would include aid workers assisting in disaster relief or refugee camps, and more adventurous backpackers who do not have access to medical care.
- Cholera comes from the Greek meaning 'flow of bile'.
- A dehydrating, diarrhoea-like death is described in both Sanskrit and Hippocrates' writings from 500-300 BC.
- Cholera became a worldwide problem in the early 19th century, with the first major pandemic of 1817-1820, spreading out of India to Europe and the Americas.
- It had long been endemic in India but, in 1817, India's traditional great Gumbo festival at Hardwar in the Upper Ganges led to vast numbers of people coming together. Steam ships were improving the ease of international travel and the disease was spread from port to port, becoming the most feared disease in the world.
- John Snow witnessed the great cholera epidemic in London in 1831-1832 when he was working as a colliery surgeon and unqualified assistant. He later became a student at the Hunterian School of Medicine in Great Windmill Street, London and two years later qualified as MRCS. He graduated MD from the University of London in 1844. In 1849 he published a small pamphlet 'On the Mode of Communication of Cholera', proposing that the 'cholera poison' reproduced in the human body and was spread through the contamination of food or water. This was opposed because the current theory was that cholera, like all infectious diseases, was transmitted through inhalation of contaminated vapours. In 1854, cholera struck England again and Snow was able to test his hypothesis that cholera was spread through contaminated food or water. He began plotting the location of deaths from cholera. London was supplied by two water companies. One company pumped its water out of the River Thames upstream of the main city while the other took its water from the river downstream from the city. A higher concentration of cholera was found in the region supplied by the water company that drew its water form the downstream location. This water was contaminated by the city's sewage. He found that near the intersection of Cambridge Street and Broad Street in Soho, up to 500 deaths from cholera occurred within 10 days. He convinced the authorities to remove the handle from the water pump in Broad Street and the infection rapidly subsided.
- The opponents of Snow argued that he had not identified the cause of the disease and it was not until some time after Snow's death that the organism was discovered by Robert Koch in 1884 during an epidemic in Egypt.
- It was understood that the remains of those who had died from cholera could spread the disease and so cholera graves were often kept apart. In York cemetery there is a specific area for cholera graves. In most cemeteries and graveyards the graves may be reused after 50 years if there is no objection from any living relative of the interred but, for cholera graves, the time is 150 years.
Further reading & references
- Thaker VV et al, Cholera, Medscape, Jul 2011
- UCLA Department for Epidemiology; Who discovered Vibrio Cholerae?
- Global epidemics and impact of cholera, World Health Organization
- Murugaiah C; The burden of cholera. Crit Rev Microbiol. 2011 Nov;37(4):337-48. Epub 2011 Aug 8.
- Cholera Fact sheet No 107, World Health Organization, August 2011
- Piarroux R, Faucher B; Cholera epidemics in 2010: respective roles of environment, strain changes, and Clin Microbiol Infect. 2012 Jan 4. doi: 10.1111/j.1469-0691.2012.03763.x.
- Cholera, National Travel Health Network and Centre
- Mahon BE, Mintz ED, Greene KD, et al; Reported cholera in the United States, 1992-1994: a reflection of global changes in cholera epidemiology. JAMA. 1996 Jul 24-31;276(4):307-12.
- Bhattacharya SK; An evaluation of current cholera treatment. Expert Opin Pharmacother. 2003 Feb;4(2):141-6.
|Original Author: Dr Gurvinder Rull||Current Version: Dr Louise Newson||Peer Reviewer: Dr Hannah Gronow|
|Last Checked: 19/04/2012||Document ID: 1951 Version: 23||© EMIS|
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