Researchers Trace The Roots Of Europe's Black Death Plague

Black Death Plague

The Black Death of the medieval era, far from being just a more dangerous form of an already-occurring disease, was a newly evolved variant of a harmless bacteria that quickly began its death march across the globe.

That's the finding of researchers who have sequenced the genome, or genetic blueprint, of plague bacteria and found that the strain arose no more than 140 years before the bubonic plague's start in 1347. The plague killed an estimated 50 million people in Europe in five years. Even more surprising, that era's plague bacteria, Yersinia pestis, don't appear to be that much more virulent than the plague of today.

Europe was in the midst of a cooling trend called the Little Ice Age, which lowered temperatures, reduced harvests and increased rains. People were ill-nourished and weak while rats flourished.

Researchers were able to extract DNA from the teeth of four skeletons excavated at a cemetery in London where more than 2,500 people were buried during the plague years. They were able to reconstruct about 99% of the plague's genome.

Plague evolved from a soil-dwelling bacteria that acquired extra genetic material, which bacteria sometimes do, and became a killing machine.

It originated in Mongolia, infecting fleas that lived on rats and quickly came into contact with a nomadic population called the Golden Horde, which was sweeping along the Silk Road trading route. They brought plague with them to Europe, where it rapidly spread, says Johannes Krause, one of the paper's authors and a paleo-archaeologist at the University of Tübingen in Germany.

The lessons for today are two-fold, he says. New diseases tend to cross over when humans move into new areas and come into contact with animals and pathogens with which they previously didn't interact. And climate change is likely to cause movement of both people and animals.

The good news is that "we have very good medical facilities and lots of researchers that can deal with this much better than they could in 1348," Poinar says. Although plague still kills an estimated 3,000 people a year mostly in the developing world, it is easily treated with antibiotics, Poinar says.