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Researchers discover source of cholera pandemic

US: Researchers tracked a deadly strain of Cholera called “El Tor” back to the Bay of Bengal. They tracked the spread of the organism by analysing the genomes of the causative bacterium Vibrio cholerae taken from 154 patients across the world over the last 40 years. Using the ability to track single DNA changes in the genome of this strain, they were able to map the transmission routes of the bacteria, aiding future health planning and enabling ‘backtracking’ of the disease to its origin.

“Looking at the past 40 years of transmissions from continent to continent, we found that the Bay of Bengal acts as a reservoir for cholera, where it can thrive and spread,” explains Nicholas Thomson from the Sanger Institute and one of the first authors of the study. “By tracking how the disease is spread, our maps of transmission could influence future decisions on how to tackle this disease.”

The study, ‘Evidence for several waves of global transmission in the seventh cholera pandemic’, recently published in the journal, Nature.

It is estimated that cholera affects 3 million to 5 million people each year, with 100,000-120,000 deaths. During the study, researchers discovered that the current strain of the bacterium — known as the El Tor strain — first became resistant to antibiotics in 1982 by acquiring the genetic region SXT, which entered the bacterium’s genome at that time, triggering renewed global transmission from the original source. Dr Julian Parkhill, a senior group leader at the Wellcome Trust Sanger Institute and a senior author of the study, said, “Our research shows the importance of global transmission events in the spread of cholera. This goes against previous beliefs that cholera always arises from local strains, and provides useful information in understanding cholera outbreaks.”

The study crucially identified the origins of the pandemic strain to its roots 40 years ago in the Bay of Bengal. From this base, it has since infected people around the world, including Africa, South Asia and South America.

This research was supported by The Wellcome Trust and The International Vaccine Institute is supported by the Governments of Korea, Sweden and Kuwait.

Source: Science Daily