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.