Plague Genome Decoded
The bacterium that caused the Black Death, one of the worst epidemics in human history, was virtually the same as the bacterium causing plague outbreaks in some parts of the world today, according to the surprising conclusion of a study of medieval skeletons. Scientists have long thought that the Black Death bacterium, called Yersina pestis, was so lethal because of certain genetic characteristics that had disappeared over the centuries. Instead, the researchers argued, other factors accounted for the Black Death’s toll. Scholars estimate that the plague killed about 30 million people, about half the population of Europe, from 1347 to 1351.
The researchers’ findings are based on a nearly complete reconstruction of the Y. pestis genome (total amount of genetic information) from DNA extracted from the teeth of three victims of the Black Death. The victims had been among 2,500 people buried in a mass grave in East Smithfield Cemetery in London. When the researchers compared the ancient Y. pestis genome to modern versions, they found that two were nearly identical.
The researchers suggested that the Black Death claimed so many victims, in part, because the immune systems of the Europeans of that time had never before been exposed to Y. pestis. “The Black Death was the first plague pandemic [widely spread epidemic] in human history,” said lead researcher Johannes Krause of the University of Tuebingen in Germany. Plague bacteria may not be as deadly to modern people because genetic mutations (changes) that allowed medieval people to survive the disease were passed down to later generations. The researchers said that the Black Death also spread so rapidly and killed so many because of miserable living conditions that included poor nutrition caused by climate change and crop failures, lack of sanitation, and war.
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