cholera

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. The worst epidemic in the Western hemisphere for 70 years occurred in Peru in 1991, with 55,000 confirmed cases and 258 deaths. It was believed to have been spread by the consumption of seafood contaminated by untreated sewage. 1991 was also the worst year on record for cholera in Africa with 13,000 deaths.

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.