Vibrio cholerae, a rod shaped bacterium.
Produces an enterotoxin that causes a severe diarrhoea that can quickly lead to severe dehydration and death if treatment is not promptly given. Most persons infected with V. cholerae do not become ill, although the bacterium is present in their faeces for 7-14 days. When illness does occur, more than 90% of episodes are of mild or moderate severity and are difficult to distinguish clinically from other types of acute diarrhoea. Less than 10% of ill persons develop typical cholera with signs of moderate or severe dehydration.
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.
Most persons infected with V. cholerae do not become ill.Symptoms generally start with copious watery diarrhea, often accompanied by vomiting, leading to dehydration. This leads to intense thirst, difficulty swallowing, muscle cramps, weakness, and the appearance that one has simply dried up.
INCIDENCE AND DISTRIBUTION
Worldwide it is endemic in at least 80 countries with epidemics occurring in various regions, including Africa, South America and South and South East Asia. In Africa alone some 79 million people are estimated to be at risk of cholera infection.
It causes 120,000 deaths a year with a concentration. The vibrio responsible for the seventh pandemic, now in progress, is known as V. cholerae O1, 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.
In 1970 cholera invaded West Africa, which had not experienced the disease for more than 100 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.
.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.
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 1%.
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.
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.
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