These skeletons—excavated in the 1980s from a 14th century graveyard in London—belonged to six of the estimated 30 million people who died from
the Black Death, the plague epidemic that swept Europe between 1347 and 1351. Researchers have now used teeth from the same graveyard—home to some
2500 plague victims—to reconstruct 99% of the genome of Yersinia pestis, the bacterium that causes plague. An analysis of that microbial DNA, published online today in Nature, suggests that Y. pestis strains currently circulating around the world are all descendents of the
medieval strain, which is believed to have killed 30% to 60% of Europe's population. The 14th century genome closely resembled those of modern strains
and did not have any obvious unique mutations that might explain its unprecedented virulence. Other factors—such as the population's susceptibility
or the ecology of rodents and fleas, which help spread the disease—were probably responsible for the medieval massacre, the team concludes.
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