Scientists finally know what killed 100,000 people in the Great Plague of London, or a quarter of the population, more than 350 years ago—and it would've been familiar to anyone around 300 years before that. An examination of 20 of the 3,500 skeletons found last year in a burial ground in the path of a new transit line shows the same bacterium responsible for the 1348 Black Death outbreak—Britain's first plague epidemic—was also responsible for the second, in 1665. "It's significant because we had this famous, severe outbreak of plague in 1665, but until very recently, there was quite a lot of doubt about what had caused it," a researcher tells the Independent.
Scientists only realized bubonic plague bacteria Yersinia pestis was responsible for the Black Death a few years ago and suspected a different disease was responsible for the Great Plague, since it appeared to act differently. Tooth pulp from five of the 20 individuals studied, however, says otherwise. "We could clearly find preserved DNA signatures in the DNA extract we made from the pulp chamber and from that we were able to determine that yersinia pestis was circulating in that individual at the time of death," a researcher tells the BBC. Worried about another outbreak? Experts note improved hygiene and antibiotics mean the risk is incredibly low, per the Londonist. (The Black Death had an upside.)