Researchers believe they have finally pinpointed the origin of the Black Death, solving a 684-year-old mystery.
The second plague pandemic, which began in the 14th century and spread across Europe, Asia and elsewhere, killed millions, upended societies and even stopped wars. For decades, researchers have followed clues and debated where the pandemic originated, with many theories but little certain evidence.
Now, a new analysis of ancient DNA extracted from a graveyard in present-day Kyrgyzstan dates the outbreak of the plague to the year 1338.
The researchers discovered DNA evidence of the bacteria that causes plague inside teeth removed from the bodies of several people buried there. The DNA is closely related to the strain that caused the Black Death less than a decade later and also to most plague strains circulating today.
“What we found in this graveyard … was the ancestor of four out of five of those lineages, so it’s really like the Big Bang of plague,” said Johannes Krause, a professor at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. at a press conference. “So we’ve basically located this origin in time and space, which is really remarkable.”
Krause and several co-authors published their findings Wednesday in the journal Nature.
The findings take some of the guesswork out of history, help researchers better understand how the plague pandemic moved around the world, and provide more insight into the conditions that allowed the Black Death to emerge. The research also highlights rapid improvements in DNA sequencing, which could help scientists study patterns of other historical diseases and prepare for future outbreaks.
Some historians have long suspected that examined burial sites in Kyrgyzstan had contained plague victims. Now, there is a physical test.
“This is concrete evidence that those people, previously suspected of having died from the plague, are known for sure to have died during the early stages of the Black Death,” said Sharon DeWitte, a bioarchaeologist and professor of the University of South Carolina. she, who has studied the black plague for two decades but was not part of this research. “I am convinced by the findings.”
The pandemic spread across Europe in the 1340s with a reputation that preceded its attack.
In London, people set aside land for a cemetery before the plague hit the city.
After hearing reports from other parts of Europe, “they knew it was inevitable that the plague would come and that a lot of people would die,” DeWitte said.
Most cities lost 30% to 60% of their population during widespread outbreaks, he said. The disease was caused by a bacterium that would later become known as Yersinia pestis.
There are several theories about how the bacteria spread in the 14th century. The most popular theory is that it was spread by biting fleas that accompanied black rats, which sometimes traveled to new places with traveling humans. Another theory blames human fleas and body lice.
The Black Death marked the beginning of the second plague pandemic, which continued for centuries.
“The pandemic lasted at least more than 400 years,” DeWitte said.
For centuries, cities continued to weather the outbreaks. Researchers differ on the end date of the pandemic. Some point to the Great Plague of London in 1665 as the end of the period, but the disease affected several other cities later.
Burial sites in present-day Kyrgyzstan, where excavations began in 1885, have piqued the curiosity of researchers for years. The sites, two Christian cemeteries, featured 467 gravestones spanning nearly 900 years, according to Philip Slavin, an author on the paper and an associate professor of history at the University of Stirling in the United Kingdom.
Some 118 of those grave markers were from 1338 and 1339, including some with inscriptions that were marked “pestilence,” but exactly what that meant has been unclear.
“Obviously, when you have a year or two with excess mortality, that means something strange is going on,” Slavin said at a recent news conference. “And 1339 is only seven or eight years before the Black Death hit Europe.”
The research team extracted seven teeth from seven people buried in the cemeteries during 1338 and 1339. The pulp of the ancient teeth is full of dried blood vessels and most likely contains evidence of blood-borne pathogens, such as the bacteria that caused the black plague
The researchers sequenced all of the ancient and degraded DNA found within the teeth and pieced together disparate strands, providing evidence for the bacteria’s presence.
Then “we were able to target the entire genome and reconstruct the entire genome from these ancient bacteria,” said Maria Spyrou, lead author of the new study and a researcher at the University of Tübingen in Germany.
The researchers found that the strain identified in the cemeteries was an ancestor of the genomes of Black Death victims some eight years later.
They also found that marmots living today in the Tian Shan mountain range near the burial site carry a closely related strain of the bacteria.
Researchers believe the Black Death strain emerged there, possibly from marmots, and then spread rapidly in the community where the burial sites were located. The community, which is near Lake Issyk-Kul in present-day Kyrgyzstan, had about 1,000 people living there before the disease hit, according to Slavin.
It was a trading post along the Silk Road, with people of many ethnicities and origins. Trade and travel probably carried the plague to other regions.
Spyrou said determining where the Black Death originated gives researchers a foothold in understanding what factors led to the pandemic.
The research was made possible, in part, by technological advances in genetic sequencing, which has become more powerful and cheaper. Future work could open doors to understand other historical disease outbreaks.
“To be able to analyze the entire genome of the strain that existed 700 years ago is extraordinary,” said DeWitte. “People are excited to look at other diseases from the past.”
Plague remains a concern today, mainly in rural areas. It can be treated with antibiotics. Improvements in hygiene have greatly reduced transmission.
Still, some countries have faced large outbreaks. Madagascar in 2017 reported more than 2,400 cases of pneumonic plague, which can spread through the air.
Krause said research into the Black Death, and the worldwide experience of the coronavirus pandemic, calls for greater emphasis on understanding what diseases animals harbor that could spread to humans.
The animal spill that caused the Black Death bears some resemblance to the diseases that make headlines today.
“We really have to increase our efforts to understand the diversity of pathogens in animal reservoirs, to monitor them,” Krause said.