The vibrio responsible for the seventh pandemic, now in progress, is known as V.cholerae Ol, biotype El Tor. The pandemic began in 1961 when the vibrio first appeared as a cause of epidemic cholera in Celebes (Sulawesi), Indonesia. The disease then spread rapidly to other countries of eastern Asia and reached Bangladesh in 1963, India in 1964, and the USSR, Iran and Iraq in 1965-1966.

Background

In 1970 cholera invaded West Africa, which had not experienced the disease for more than l00 years. The disease quickly spread to a number of countries and eventually became endemic in most of the continent. In 1991 cholera struck Latin America, where it had also been absent for more than a century. Within the year it spread to 11 countries, and subsequently throughout the continent.

Until 1992, only V. cholerae serogroup O1 caused epidemic cholera. Some other serogroups could cause sporadic cases of diarrhoea, but not epidemic cholera. Late that year, however, large outbreaks of cholera began in India and Bangladesh that were caused by a previously unrecognized serogroup of V. cholerae, designated O139, synonym Bengal. Isolation of this vibrio has now been reported from l0 countries in South Asia. It is still unclear whether V cholerae Ol39 will extend to other regions, and careful epidemiological monitoring of the situation is being maintained.

Transmission

Cholera is spread by contaminated water and food. Sudden large outbreaks are usually caused by a contaminated water supply. Only rarely is cholera transmitted by direct person-to-person contact. In highly endemic areas it is mainly a disease of young children, although breastfeeding infants are rarely affected.

Marine shellfish and plankton are the main reservoirs of V cholerae. The El Tor strain can also survive in fresh water for long periods. Persons with asymptomatic infections play an important role in carrying V, cholerae from place to place, causing epidemics to spread.

Treatment

When cholera occurs in an unprepared community, case-fatality rates may be as high as 50% — usually because there are no facilities for treatment, or because treatment is given too late. In contrast, a well organized response in a country with a well established diarrhoeal disease control programme can limit the case-fatality rate to less than I%.

Most cases of diarrhoea caused by V, cholerae can be treated adequately by giving a solution of oral rehydration salts. During an epidemic, 80-90% of diarrhoea patients can be treated by oral rehydration alone, but patients who become severely dehydrated must be given intravenous fluids.

In severe cases, an effective antibiotic can reduce the volume and duration of diarrhoea and the period of vibrio excretion. Tetracycline is the usual antibiotic of choice, but resistance to it is increasing. Other antibiotics that are effective when V.cholerae are sensitive to them include cotrimoxazole, erythromycin, doxycycline, chloramphenicol and Furazolidone.

Epidemic Control and Preventative Measures

When cholera appears in a community it is essential to ensure three things: hygienic disposal of human faeces, an adequate supply of safe drinking water, and good food hygiene. Effective food hygiene measures include cooking food thoroughly and eating it while still hot; preventing cooked foods from being contaminated by contact with raw foods, contaminated surfaces or flies; and avoiding raw fruits or vegetables unless they are first peeled.

Routine treatment of a community with antibiotics, or “mass chemoprophylaxis”, has no effect on the spread of cholera, nor does restricting travel and trade between countries or between different regions of a country. Setting up a cordon sanitaire at frontiers uses personnel and resources that sh.ould be devoted to effective control measures, and hampers collaboration between institutions and countries that should unite their efforts to combat cholera.

The only cholera vaccine that is widely available at present is killed vaccine administered parenterally, which confers only partial protection (50% or less) and for a limited period of time (3-6 months maximum). Use of this vaccine to prevent or control cholera outbreaks is not recommended because it may give a false sense of security to vaccinated subjects and to health authorities, who may then neglect more effective measures,

In 1973 the World Health Assembly deleted from the International Health Regulations the requirement for presentation of a cholera vaccination certificate. Today, no country requires proof of cholera vaccination as a condition for entry, and the lnternational Certificate of Vaccination no longer provides a specific space for recording cholera vaccinations.

Limited stocks of two oral cholera vaccines that provide high-level protection for several months against cholera caused by V.cholerae Ol have recently become available in a few countries. Both are suitable for use by travellers. In the acute phase of an emergency, priority should be given to basic relief activities, including provision of food, clean water, shelter and basic medical care. When a cholera epidemic occurs in this phase, efforts should focus on providing treatment, safe water and basic sanitation. Cholera vaccination in this situation is not likely to be useful, and is not recommended.