The bacteria that cause tuberculosis emerged at least 70,000 years ago and followed humans out of Africa, suggests new research.
From there, TB tagged along on human migrations and evolved as people changed. The new findings offer insight into a disease that kills as many as 2 million people every year and is increasingly developing resistance to drugs designed to treat it.
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"The evolutionary path of humans and the TB bacteria shows striking similarities," said Sebastien Gagneux from the Swiss Tropical and Public Health Institute in a press release. "We see that the diversity of tuberculosis bacteria has increased markedly when human populations expanded."
Between the 17th and 19th centuries, TB killed 20 percent of adults in Europe and North America. Even today, it remains one of the deadliest infectious diseases in humans, particularly in developing countries. When untreated, it kills half of all people it infects.
To better understand the history of TB, Gagneux and colleagues sequenced and compared the genomes of 259 strains of the M. tuberculosis bacteria from around the world. Then they reconstructed a TB family tree, which allowed them to trace back the origins of the disease to somewhere in Africa about 70,000 years ago.
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When the researchers compared the TB family tree with the history of human migrations, they reported in the journal Nature Genetics, they found remarkable similarities. The disease split into branches at the same time that waves of hunter-gatherers left Africa and moved into Europe and Asia.
A boom in human population around 10,000 years ago also coincided with the expansion of TB, probably because denser groups of people allowed the disease to spread more easily.
TB "has been coevolving with anatomically modern humans for tens of thousands of years," changing and adapting alongside people, the researchers wrote. "Exploration of the changes that have occurred in this interaction over time may help to predict future patterns of disease and to design rational strategies to bring an end to this historic partnership."
Photo: Electron micrograph of Mycobacterium tuberculosis. Credit: Corbis