FRIDAY, SEPTEMBER 30, 2016

Scientists discover new secrets about TB

A team of scientists led by University of Wisconsin-Madison researcher Caitlin Pepperell released findings on Wednesday that detail why TB is so prevalent and why it is able to evolve to resist efforts to fight the disease.

The scientists found that TB is able to follow human behavior and patterns in order to take advantage of the worst possible human conditions.

"It's as though the bacterium places bets on human behavior," Pepperell said. "It always bets that humans will go to war, send people to refugee camps, and gather in miserable places. Historically, that's been a winning bet on the bacterium's part."

The study looked at periods of time when TB showed a 25-fold expansion worldwide. This happened in the 17th century when human populations were experiencing a large amount of growth and explorations of new lands were at their peaks.

"The timing is coincident with expansion, urbanization and colonial migrations of global human populations," Pepperell said. "These findings suggest that much of the current TB pandemic has its origins in historical events of the last three centuries."

The scientists then looked at genetic diversity among 63 TB genomes gathered from around the world. They found that the bacterial genome is highly constrained, with most mutations quickly discarded. This did not hold true in TB's defense genes, however, which showed a high tolerance for mutation.

"Evolutionary theory predicts that Mycobacterium tuberculosis populations should be vulnerable to extinction," Pepperell said. "Yet it is obviously highly prevalent. It must have some incredibly clever strategies and tricks to hang on."