Deadly TB strains emerged in Asia over 6,000 years ago

In a path-breaking find, an evolutionary geneticist from the National Museum of Natural History in Paris has decoded the tuberculosis (TB) genome, suggesting that a pernicious family of the strain emerged in Asia over 6,000 years ago.

The study of nearly 5,000 samples of Mycobacterium tuberculosis from around the world showed how a lineage of the bacterium that emerged thousands of years ago in China has since become a global killer, widely resistant to antibiotic drugs, the Nature Genetics reported.

The evolutionary geneticist Thierry Wirth and his team analysed 4,987 samples of the "Beijing lineage" from 99 countries, fully sequencing the genomes of 110 of them and more limited stretches of DNA in the rest.

The researchers then used the information to date the expansion of the lineage and show how the strains are related.

Consistent with its name, the "Beijing lineage" did emerge near north-eastern China."And it did so around 6,600 years ago which coincides with archaeological evidence for the beginnings of rice farming in China's upper Yangtze river valley," Wirth noted.

Although M. tuberculosis, probably, first emerged some 40,000 years ago in Africa, the disease did not take hold until humans took to farming with the consequent settling down.

"The grouping of people in settlements made it easier for the respiratory pathogen to spread from person to person," Wirth pointed out.

Of all the M. bacterium strains circulating today, few strike more fear in public-health officials than the Beijing lineage.

First identified in greater Beijing in the mid-1990s, this lineage now circulates throughout the world and many strains are resistant to drugs that vanquish other types of TB.

The increasing availability of antibiotics in the 1960s, meanwhile, coincides with a fall in the numbers of the bacterium.

The lineage rebounded, however, in the late 1980s and early 1990s.

Since it emerged, the "Beijing lineage" has become much more infectious, Wirth says, so it out-competes other strains of the bacterium.

His team identified mutations related to antibiotic resistance, metabolism and evasion of immune responses that may have contributed to the success of the "Beijing lineage".