Black Death's origin is identified at last

BLACK Death rampaged across Europe in 1348, killing a third of the population. Now the complete sequence of Yersinia pestis, the most likely cause of the Black Death, has been unearthed from a medieval mass grave in London.

“The DNA from 1348 had telltale changes showing that it was indeed an ancient form of Yersinia”

The mystery over the disease continues, however, as modern Yersinia infection – which causes bubonic plague – behaves very differently to the Black Death, yet its DNA is virtually unchanged.

“This is the first time a human pathogen more than a century old has ever been fully sequenced,” says Johannes Krause at the University of Tübingen, Germany. The teams used DNA from modern Yersinia in an array that bound to similar DNA in victims’ teeth. That DNA carried telltale chemical changes showing it was indeed ancient plague. Differences reported earlier between it and modern Yersinia were not confirmed.

The sequence also shows the ancient bacteria started infecting humans at the right time, between 1240 and 1340, just before the disease exploded (Nature, DOI: 10.1038/nature10549).

Yersinia has for some time been the prime suspect because some of its symptoms are similar to the Black Death. But questions were raised because modern Yersinia is a slow-spreading, rat-borne disease that is very different from the Black Death. Its DNA doesn’t explain why. “There are almost no genetic differences between the ancient and modern Yersinia,” says Krause.

He speculates that the Black Death behaved differently from modern Yersinia infection due to Europeans’ total lack of previous exposure. Another possibility is co-infection with other pathogens, a so-called syndemic. The team hopes to learn more about the evolution of human disease by probing plague pits and other ancient samples for different pathogens.