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The Spread of TB

The growth and spread of Mycobacterium tuberculosis parallels that of the human race, a new study in PLOS Pathogens says. The University of Wisconsin-Madison's Caitlin Pepperell and her colleagues examined sequence data from more than 60 TB strains to search for evidence of positive and negative selections as well as any regional differences in selection.

Within these TB genomes, they found hints of both positive and purifying selection. In particular they found that genes linked to the transportation and metabolism of inorganic ions had low levels of non-synonymous polymorphisms while a group of transporter genes high levels of non-synonymous polymorphisms, which the researchers suspect might be because of diversifying selection or local selective sweeps.

Additionally, Pepperell and her colleagues note that the TB population underwent explosive growth in the 17th century — right around when people were undergoing a similar population growth and when European exploration of the globe was at its peak. "The timing is coincident with expansion, urbanization and colonial migrations of global human populations," Pepperell says in a statement. "These findings suggest that much of the current TB pandemic has its origins in historical events of the last three centuries."