Evolution of new variants of Vibrio cholerae
Cholera, a severe form of acute secretory diarrhoea, is caused by the gamma-proteobacterium Vibrio cholerae. Pathogenic strains harbour a cholera toxin prophage (CTXΦ) that carries the genes that encode the cholera toxin (CT), a key virulence factor that is directly responsible for the major clinical symptoms of the disease. CT binds to a specific receptor (GM1) on host enterocytes and is internalized, leading to elevated intracellular cAMP levels and resulting in a major loss of water and electrolytes in profuse secretory diarrhoea. To date, >200 serogroups (a sub-species taxonomic classification) of V. cholerae have been identified, based on variations in O-antigen structure. Most of the clinical strains belonging to serogroups O1 and O139 are toxigenic, and are responsible for all the major cholera epidemics and pandemics on record. Conversely, strains belonging to other serogroups (collectively known as ‘non-O1/non-O139’) are rarely toxigenic (<1%) and have seldom caused epidemics. Therefore, it appears that the ability to produce CT is essential if the disease is to result in major cholera epidemics.
Evolution of new variants of Vibrio cholerae O1. Trends Microbiol. Nov 24 2009
Vibrio cholerae typically contains a prophage that carries the genes encoding the cholera toxin, which is responsible for the major clinical symptoms of the disease. In recent years, new pathogenic variants of V. cholerae have emerged and spread throughout many Asian and African countries. These variants display a mixture of phenotypic and genotypic traits from the two main biotypes (known as ‘classical’ and ‘El Tor’), suggesting that they are genetic hybrids. Classical and El Tor biotypes have been the most epidemiologically successful cholera strains during the past century, and it is believed that the new variants (which we call here ‘atypical El Tor’) are likely to develop successfully in a manner similar to these biotypes. Here, we describe recent advances in our understanding of the epidemiology and evolution of the atypical El Tor strains.
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Tags: Bacteria, Biology, disease, Health, Medicine, Microbiology, Science, Virology, virus
