Tuesday, November 15, 2016

Pandemic cholera evolution

Scimex: Researchers report the evolutionary origins of the current cholera pandemic. The current cholera pandemic, the seventh since 1817, began in Indonesia in 1961 and currently infects 3-5 million people annually. Dalong Hu et al. obtained complete genome sequences of four Vibrio cholerae strains isolated during the first few years of the pandemic, as well as three related strains from pre-pandemic cholera outbreaks and three strains from outbreaks in the 1970s that are more closely related to the pre-pandemic strains than to the pandemic strains.
These genomes were combined with previously published genomes and historical data to trace the evolutionary history of the V. cholerae lineage responsible for the current pandemic. The authors identified six stages in the evolution of the seventh pandemic strain, which likely originated as a non-pathogenic strain in South Asia. This strain was introduced to the Middle East in the 1890s, possibly by religious pilgrims, where it underwent rapid diversification, becoming pathogenic by 1908. The strain then migrated to Indonesia between 1908 and 1925, where it acquired substantial genetic changes culminating in the acquisition of pandemic spreading capability between 1954 and 1960. The pandemic lineage passed through areas that had seen previous cholera pandemics, which might have facilitated evolution of the seventh pandemic strain by enabling it to acquire genes from previous pandemic strains.