Cholera is an acute gastro-intestinal illness caused by the ingestion of the bacterium Vibrio cholerae. There are over 100 serotypes of V. cholerae but only two cause disease (O1 and O139). It is a water-borne infection found in faecally contaminated water sources. Cholera is also commonly contracted by eating contaminated seafood or food that has become contaminated by being handled or prepared by someone with the disease. Fruit and vegetables have also been contaminated when land has been irrigated with raw sewage. Humans are the only known natural hosts.
It is characterised in its most severe form by a sudden onset of acute watery diarrhoea that can lead to death by severe dehydration. The extremely short incubation period – two hours to five days – enhances the potentially explosive pattern of outbreaks, as the number of cases can rise very quickly. About 75% of people infected with cholera do not develop any symptoms. However, the pathogens stay in their faeces for 7 to 14 days and are shed back into the environment, possibly infecting other individuals. Cholera is an extremely virulent disease that affects both children and adults. Unlike other diarrhoeal diseases, it can kill healthy adults within hours. Individuals with lower immunity, such as malnourished children or people living with HIV/AIDS, are at greater risk of death if infected by cholera.
A vaccine is available that is effective against cholera but it is not indicated for most travellers. However, it can be offered to humanitarian aid and relief workers and travellers with remote itineraries in areas of cholera outbreaks who have limited access to safe water and medical care.
Cholera can range in severity from a mild illness that may show no symptoms, through to very severe symptoms. The first signs are nausea and discomfort in the abdomen, followed by sudden watery diarrhoea and vomiting. Vomiting tends to disappear after around 12 hours, although the diarrhoea may continue. Cholera often causes people to painlessly lose large amounts of liquid stools, up to 20 litres a day – often called “rice water” stools because of their appearance. People with cholera often have extremely painful muscle cramps.
If cholera is left untreated, severe dehydration and “hypovolaemic” shock can happen, following overwhelming fluid loss. Severe untreated cholera can cause kidney failure and in 50% of cases, death. In children, low blood sugar can occur which can be severe and cause convulsions and coma. In pregnant women, cholera can cause miscarriages and premature birth.
Cholera can be confirmed by testing a sample of a patient’s stools in a laboratory. Rapid tests are also being developed which do not need to be done in laboratories. However, where there are outbreaks of large numbers of cases, laboratory tests would not be carried out on all patients and doctors would be able to diagnose patients based on their diarrhoea and vomiting symptoms.
As previously mentioned, if cholera is not treated, up to 50% of symptomatic people can die. However, as long as treatment is given, this is reduced to around 1% of cases. Rapidly rehydrating patients is the most important treatment for cholera. Drinking oral rehydration salt solution can rehydrate the majority of cases. Severely dehydrated patients will need intravenous fluids and may also be treated with antibiotics. Infection control measures are important with cholera patients, because the bacteria are highly infectious. Patients in hospital or being cared for at home, should be isolated and strict hygiene measures implemented to reduce the risk of spreading the infection.
Cholera is a disease that occurs in low-income regions of the world where sanitation and food and water hygiene are inadequate. Imported cases occasionally occur in travellers returning from endemic areas.
In areas without clean water or sewage disposal (as may occur after natural disasters or in displaced populations in areas of conflict), cholera can spread quickly and have a case fatality rate of as high as 50% in vulnerable groups with limited medical care. The most common risk factors for cholera are water source contamination, heavy rainfall and flooding and population dislocation. It is most common in South East Asia, particularly the Indian sub-continent, although outbreaks have also happened in other parts of the world including current outbreaks in sub-Saharan Africa and Latin America. It affects all ages but children are at the highest risk for acquiring severe disease.
Every year there are an estimated 3–5 million cholera cases and 100,000–120,000 deaths due to the disease. The World Health Organization (WHO) reports the emergence of new, apparently more virulent, strains of V. cholerae that now predominate in parts of Africa and Asia, and the emergence and spread of antibiotic resistant strains.
- Cholera is an acute diarrhoeal disease that can kill within hours if left untreated
- There are an estimated 3–5 million cholera cases and 100,000–120,000 deaths due to cholera every year
- Up to 80% of cases can be successfully treated with oral rehydration salts
- Effective control measures rely on prevention, preparedness and response
- Provision of safe water and sanitation is critical in reducing the impact of cholera and other waterborne diseases
- Oral cholera vaccines are considered an additional means to control cholera but should not replace conventional control measures.
Measures for the prevention of cholera mostly consist of providing clean water and proper sanitation to populations who do not yet have access to basic services. Health education and good food hygiene are equally important. Communities should be reminded of basic hygienic behaviours, including the necessity of systematic hand washing with soap after defecation and before handling food or eating, as well as safe preparation and conservation of food.
Once an outbreak is detected, the usual intervention strategy is to reduce deaths by ensuring prompt access to treatment and to control the spread of the disease by providing safe water, proper sanitation and health education for improved hygiene and safe food handling practices by the community. The provision of safe water and sanitation is a formidable challenge but remains the critical factor in reducing the impact of cholera. In order to ensure timely access to treatment, cholera treatment centres (CTCs) should be set up among the affected populations. With proper treatment, the case fatality rate should remain below 1%.
Conversely, routine treatment of a community with antibiotics, or mass chemoprophylaxis, has no effect on the spread of cholera and can have adverse effects by increasing antimicrobial resistance and providing a false sense of security.
History of Cholera
During the 19th century, cholera spread across the world from its original reservoir in the Ganges delta in India. Six subsequent pandemics have killed millions of people across all continents. Until the mid-20th century it was largely confined to Asia. The current (seventh) pandemic started in Indonesia in 1961, and reached West Africa in 1971 and then spread to Peru in 1991 and subsequently most of Latin America. Another serogroup was discovered as the cause of cholera epidemics in India and Bangladesh in 1992 and has since spread to other countries in South East Asia and China.
Cholera is now endemic in many countries – 58 countries reported cholera cases to WHO in 2011, ten more than the previous year. The worst cholera epidemic in recent history began in Haiti in October, 2010. By August 2012, more than 7,500 people had died and almost 600,000 cases were recorded. Published research and a UN investigation suggest that the UN military mission, MINUSTAH, was the most likely source, caused by failures in medical screening and waste management.
In Africa in 2011, 27 countries reported a total of 189,000 cases (including over 4,000 deaths). The majority of cases were reported from four countries (Cameroon, Democratic Republic of Congo, Nigeria and Somalia).
Asia reported a total of 38,000 cases in 15 countries; the greatest number of cases were reported from Afghanistan and Iran.
In Europe, Ukraine reported 33 cases during May and June 2011. Although Ukraine is not classified as an endemic country, cholera had previously been reported there in 2005 (1 case) and during 1994-5 (1,370 cases and 32 deaths).
Recently, new variant strains have been detected in several parts of Asia and Africa. Observations suggest that these strains cause more severe cholera with higher case fatality rates. Globally, mortality and morbidity relating to cholera is likely to be grossly under-reported due to the limitations of surveillance and reporting systems. The large numbers of “acute watery diarrhoea”, estimated to number between 500,000-700,000 cases globally each year of which many may be cholera, are not included in WHO cholera reports.