When the plague swept through Europe in 1665, no one could figure out how the devastating disease spread. But after a tailor in the small village of Eyam in central England died that September, people eventually put two and two together. He had received a parcel of cloth infested with fleas just 4 days before dying of bubonic plague. Within a month, five other villagers had succumbed, and the local vicar convinced the town to voluntarily put itself under quarantine. It eventually became clear that it was fleas, probably on rats, that spread the plague so far and so quickly.
But now it appears that the plague did not always infect fleas—and the disease may not have always spread so rapidly or been as devastating. A new study of ancient DNA from the teeth of 101 Bronze Age skeletons has found that seven people living 2800 to 5000 years ago in Europe and Asia were infected with Yersinia pestis, the bacteria that causes the plague. But their strains of Y. pestis were missing a gene that allowed it to infect fleas, according to the study published today in Cell. This pushes back the earliest evidence of the plague by almost 3300 years and offers a key clue about how this disease became so contagious. “It’s really cool that they can pinpoint the acquisition of key genes that allow the movement of this bacteria into fleas,” says evolutionary geneticist Hendrik Poinar of McMaster University in Hamilton, Canada, who was not involved with the study.
The plague has caused death and destruction in Europe at least since Roman times, launching at least three major pandemics that changed the course of history—the Plague of Justinian from 541 to 544, which weakened the Byzantine Empire; the Black Death, which killed almost half the population of Europe between 1347 and 1351; and the Great Plague of 1665, which lasted more than 30 years. Ancient DNA researchers have shown in recent years that Y. pestis caused all three of those pandemics. But until now, they were unable to determine whether Y. pestis caused reported plagues 2224 years ago in China and almost 2500 years ago in Greece. They suspected that ancient versions of the plague were not as devastatingly rapid in spread, but they could not test that idea because they lacked samples of the earlier pathogens.
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