Historians know all about the devastation wrought by the Black Death, the bubonic plague that swept through Eurasia and killed tens of millions of people in the mid-1300s. But when it comes to certain basic questions about its origins, they’ve remained stumped.
Now, scientists may have some answers. After analyzing DNA traces found in the teeth of plague victims, researchers argue that the Black Death started in what is now northern Kyrgyzstan. Their findings, published this week in Nature, suggest that the Black Death then spread to Europe via trade routes.
“This is the place where it all started—the Wuhan of the Black Death,” Johannes Krause, a paleogeneticist with the Max Planck Institute for Evolutionary Anthropology and one of the study’s authors, tells Science’s Ann Gibbons.
The Black Death, which killed an estimated 30 to 50 percent of Europe’s population, is named for the black spots that formed on its victims’ bodies. The disease killed quickly, causing painfully swollen lymph nodes (called buboes), fevers, vomiting, delirium and other unpleasant symptoms. People can still get plague today, but it’s easily treatable with antibiotics—and because hygiene has improved since the 14th century, it is quite rare.
Finding the disease’s origin “is like a detective story,” says Mary Fissell, a medical historian at Johns Hopkins University, to the New York Times’ Gina Kolata. “Now they have really good evidence of the scene of the crime.”
Like sleuths trying to solve any complex mystery, the researchers relied on a number of clues. Their main source of evidence: the bodies of three women buried in the cemetery of a medieval community near Lake Issyk Kul in the foothills of the Tian Shan mountains, reports Reuters’ Will Dunham.
The women’s gravestones included the year of their deaths—1338 and 1339—and said they had died of “pestilence.” Researchers also noted that many other tombstones bore those dates, which are seven or eight years before the plague reportedly arrived in Europe.
When the researchers tested DNA extracted from the pulp of the plague victims’ teeth, they made an incredible find: an ancient strain of Yersinia pestis, the bacterium responsible for the Black Death.
As Monica Green, a medical historian and independent scholar, tells the Times, this finding “puts a pin in the map, with a date.”
Marmots living in the area today have fleas that carry a strain of the bacterium—and the researchers say that this strain is likely related to the ancient strain. For this reason, they hypothesize that marmots were responsible for transmitting the disease to humans.
The DNA also helped solve a genetic puzzle that had been perplexing researchers. Several years ago, scientists used ancient DNA analysis to build a genetic family tree of the plague, showing how its various strains evolved over time. Around the time of the Black Death, the bacterium suddenly branched out into four strains, an event researchers coined the “big bang.” One of those strains likely caused the Black Death and subsequent outbreaks in Europe.
Now, the researchers say that the strain found in Kyrgyzstan is the trunk of the family tree, or the “mother” strain, per Science. From that strain came most of the plague bacteria that still exist today.
“Just like Covid, the Black Death was an emerging disease, and the start of a huge pandemic that went on for some 500 years,” Krause tells CNN’s Katie Hunt. “It's very important to understand actually in what circumstances did it emerge.”