Researchers believe they have solved the nearly 700-year-old mystery of the origins of the Black Death, the deadliest pandemic in recorded history that swept through Europe, Asia and North Africa in the mid-14th century.
At least tens of millions of people died as the bubonic plague swept across continents, likely spreading along trade routes. Despite intensive efforts to uncover the source of the outbreak, the lack of clear evidence has left the question open.
“We have essentially localized the origin in time and space, which is really remarkable,” said Prof. Johannes Krause from the Max Planck Institute for Evolutionary Anthropology in Leipzig. “Not only have we found the ancestor of the Black Death, but also the ancestor of most of the plague strains circulating in the world today.”
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The international team came together to work on the mystery when Dr. Philip Slavin, a historian at the University of Stirling, uncovered evidence of a sudden increase in deaths in the late 1330s in two cemeteries near Lake Issyk Kul in northern modern Kyrgyzstan.
Among 467 tombstones dated between 1248 and 1345, Slavin traced a huge increase in deaths, with 118 stones dated to 1338 or 1339. Inscriptions on some tombstones mentioned the cause of death as “mawtānā”, the Syriac term for “plague”.
The epitaph on this tombstone, written in Syriac, reads: “In the year 1649 [AD 1337-8], and it was the year of the tiger. This is the tomb of the believer Sanmaq. [He] died of the plague.’ Photo: AS Leybin, August 1886Further investigation revealed that the sites had been excavated in the late 1880s and about 30 skeletons were removed from their graves. After studying the diaries of the excavations, Slavin and his colleagues traced some of the remains and linked them to specific tombstones in the cemeteries.
The study then passed to ancient DNA specialists, including Krause and Dr. Maria Spyrou at the University of Tübingen in Germany. They extracted genetic material from the teeth of seven people buried in the cemeteries. Three of them contained DNA from Yersinia pestis, the bacterium that causes bubonic plague.
A full analysis of the bacterium’s genome revealed that it was a direct ancestor of the strain that caused the Black Death in Europe eight years later, and as a result was likely the cause of death for more than half the population of the next decade or so.
The tribe’s closest living relative has now been found in rodents in the same region, the scientists said. While people are still being infected with bubonic plague, better sanitation and less contact with rat fleas, which can transmit the infection to humans, have prevented further deadly plague epidemics.