Disease caused by infection with various strains of the bacillus Vibrio cholerae, transmitted in contaminated water and characterized by violent diarrhoea and vomiting. It is prevalent in many tropical areas.
The formerly high death rate during epidemics has been much reduced by treatments to prevent dehydration and loss of body salts, together with the use of antibiotics. There is an effective vaccination that must be repeated at frequent intervals for people exposed to continuous risk of infection.
Since 2005, the World Health Organization (WHO) has recorded rising numbers of cholera cases, which the organization blames on increasing sizes of populations living in unsanitary conditions. One of the worst epidemics in recent times occurred in Zimbabwe in 2008–09, with over 98,000 cases and 4,200 deaths reported to the WHO by May 2009.
The sequencing of the complete cholera genome was completed in 2000, revealing that the pathogen has two circular chromosomes, while most kinds of bacteria have only one. Many of the genes that enable cholera to attack humans are found on the larger chromosome, which carries around 75% of the genes. The discovery should aid the development of a more effective vaccine and other drugs to combat the disease.
In 1996 US researchers revealed that infection by a virus (a bacteriophage) can convert a benign variant of V. cholerae into a virulent form. The gene that codes for the cholera toxin is carried by a virus, and when this virus infects V. cholerae that already contain genes for the pili (hairs) that allow bacteria to cling to each other and to host cells, the resulting strain becomes virulent.
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