Cholera is an acute diarrhoeal infection caused by ingestion of food or water contaminated with the bacteriumVibrio cholerae. Cholera remains a global threat to public health and an indicator of inequity and lack of social development. Researchers have estimated that every year, there are roughly 1.3 to 4.0 million cases, and 21 000 to 143 000 deaths worldwide due to cholera1.
Symptoms
Cholera is an extremely virulent disease that can cause severe acute watery diarrhoea. It takes between 12 hours and 5 days for a person to show symptoms after ingesting contaminated food or water2. Cholera affects both children and adults and can kill within hours if untreated.
Most people infected with V. cholerae do not develop any symptoms, although the bacteria are present in their faeces for 1-10 days after infection and are shed back into the environment, potentially infecting other people.
Among people who develop symptoms, the majority have mild or moderate symptoms, while a minority develop acute watery diarrhoea with severe dehydration. This can lead to death if left untreated.
History
During the 19th century, cholera spread across the world from its original reservoir in the Ganges delta in India. Six subsequent pandemics killed millions of people across all continents. The current (seventh) pandemic started in South Asia in 1961, and reached Africa in 1971 and the Americas in 1991. Cholera is now endemic in many countries.
Vibrio cholerae strains
There are many serogroups of V. cholerae, but only two – O1 and O139 – cause outbreaks. V. cholerae O1 has caused all recent outbreaks. V. cholerae O139 – first identified in Bangladesh in 1992 – caused outbreaks in the past, but recently has only been identified in sporadic cases. It has never been identified outside Asia. There is no difference in the illness caused by the two serogroups.
The main reservoirs of V. cholerae are people and aquatic sources that are somewhat salty and warm such as estuaries and some coastal areas. Recent studies indicate that climate change creates a favourable environment for the bacteria that causes cholera3.
Epidemiology, risk factors, and disease burden
Cholera can be endemic or epidemic. A cholera-endemic area is an area where confirmed cholera cases were detected during 3 out of the last 5 years with evidence of local transmission (meaning the cases are not imported from elsewhere). A cholera outbreak/epidemic is defined by the occurrence of at least 1 confirmed case of cholera with evidence of local transmission in an area where there is not usually cholera.
Cholera transmission is closely linked to inadequate access to clean water and sanitation facilities. Typical at-risk areas include peri-urban slums, where basic infrastructure is not available, as well as camps for internally displaced persons or refugees, where minimum requirements of clean water and sanitation have not been met.
The consequences of a humanitarian crisis – such as disruption of water and sanitation systems, or the displacement of populations to inadequate and overcrowded camps – can increase the risk of cholera transmission, should the bacteria be present or introduced. Uninfected dead bodies have never been reported as the source of epidemics.
The number of cholera cases reported to WHO has continued to be high over the last few years. During 2015,172 454 cases were notified from 42 countries, including 1304 deaths4. The discrepancy between these figures and the estimated burden of the disease is due to the fact that many cases are not recorded due to limitations in surveillance systems and fear of impact on trade and tourism.
Prevention and control
A multifaceted approach is key to prevent and control cholera, and to reduce deaths. A combination of surveillance, water, sanitation and hygiene, social mobilisation, treatment, and oral cholera vaccines are used.
Surveillance
Cholera surveillance should be part of an integrated disease surveillance system that includes feedback at the local level and information-sharing at the global level.
Cholera cases are detected based on clinical suspicion in patients who present with severe acute watery diarrhoea. The suspicion is then confirmed by identifying V. choleraein stool samples from affected patients. Local capacity to detect (diagnose) and monitor (collect, compile, and analyse data) cholera occurrence is central to an effective surveillance system and to plan control measures.
Countries neighbouring cholera-affected areas are encouraged to strengthen disease surveillance and national preparedness to rapidly detect and respond to outbreaks should cholera spread across borders. Under the International Health Regulations, notification of all cases of cholera is no longer mandatory. However, public health events involving cholera must always be assessed against the criteria provided in the regulations to determine whether there is a need for official notification.
Water and sanitation interventions
The long-term solution for cholera control (which benefits all diseases spread by the fecal-oral route) lies in economic development and universal access to safe drinking water and adequate sanitation. These measures prevent both epidemic and endemic cholera.
Actions targeting environmental conditions include:
the development of piped water systems with water treatment facilities (chlorination)interventions at the household level (water filtration, chemical or solar disinfection of water, safe water storage)the construction of systems for safe sewage disposal, including latrines.
Many of these interventions require substantial long-term investments and continued maintenance, making them difficult to fund and sustain by less developed countries where the interventions are most needed.
Treatment
Cholera is an easily treatable disease. The majority of people can be treated successfully through prompt administration of oral rehydration solution (ORS). The WHO/UNICEF ORS standard sachet is dissolved in 1 litre (L) of clean water. Adult patients may require up to 6 L of ORS to treat moderate dehydration on the first day.
Severely dehydrated patients are at risk of shock and require the rapid administration of intravenous fluids. A 70 kg adult will require at least 7 L of intravenous fluid, plus ORS during their treatment. These patients are also given appropriate antibiotics to diminish the duration of diarrhoea, reduce the volume of rehydration fluids needed, and shorten the amount and duration of V. choleraeexcretion in their stool.
Mass administration of antibiotics is not recommended, as it has no proven effect on the spread of cholera and contributes to increasing antimicrobial resistance.
Rapid access to treatment is essential during a cholera outbreak. Oral rehydration should be available in communities, in addition to larger centres that can provide intravenous fluids and 24 hour care. With early and proper treatment, the case fatality rate should remain below 1%.
Hygiene promotion and social mobilisation
Health education campaigns, adapted to local culture and beliefs, should promote the adoption of appropriate hygiene practices such as hand-washing with soap, safe preparation and storage of food and safe disposal of the faeces of children. Funeral practices for individuals who die from cholera must be adapted to prevent infection among attendees. Breastfeeding should also be promoted.
Further, awareness campaigns should be organised during outbreaks, and information should be provided to the community about the potential risks and symptoms of cholera, precautions to take to avoid cholera, when and where to report cases and to seek immediate treatment when symptoms appear. The location of appropriate treatment sites should also be shared.
Oral cholera vaccines
Currently there are 3 WHO pre-qualified oral cholera vaccines: Dukoral, Shanchol, and Euvichol. All 3 vaccines require 2 doses for full protection 5.
Dukoral is administered with a buffer solution that, for adults, requires 150 ml of clean water. As access to clean water is often limited in areas with cholera epidemics, Dukoral is mainly used for travellers. Dukoral provides approximately 65% protection against cholera for 2 years.
Shanchol and Euvichol are essentially the same vaccine produced by 2 different manufacturers. They do not require a buffer solution for administration, which makes them easier to administer to large numbers of people in emergency contexts. There must be a minimum of 2 weeks delay between each dose of these 2 vaccines. However, 1 dose of vaccine will provide some protection with the second dose given at a later date.
Individuals vaccinated with Shanchol or Euvichol have approximately 65% protection against cholera for up to 5 years following vaccination in endemic areas. The reduced circulation of V. cholerae bacteria in the population due to the reduced number of people with cholera further reduces cholera in the population. This additional protection is called herd protection.
In 2013, WHO established a stockpile of 2 million doses for use in outbreak control and emergencies. The stockpile is managed by the International Coordinating Group (ICG) made up of the International Federation of Red Cross and Red Crescent Societies, Medecins Sans Frontieres, UNICEF, and WHO.
For non-emergency settings, vaccines are available via the Global Task Force on Cholera Control (see WHO response section below). In these contexts, oral cholera vaccines (OCVs) are used as part of a longer-term cholera control plan including reinforcement of other aspects of cholera control. In eligible countries, financial support for vaccines is provided by Gavi, the Vaccine Alliance.
Ref: WHO
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