Ancient teeth offer new insight into how the Black Death emerged and spread globally

Ancient teeth offer new insight into how the Black Death emerged and spread globally

Researchers believe they have finally identified the origin of the Black Death, solving a 684-year-old mystery.

The second plague pandemic, which began in the 14th century and swept across Europe, Asia and elsewhere, killed millions, toppled societies and even stopped wars. For decades, researchers have chased clues and debated where the pandemic originated, with many theories but little certain evidence.

Now, a new analysis of ancient DNA taken from a cemetery in modern Kyrgyzstan dates the outbreak of the plague to the year 1338.

The researchers found evidence of DNA from the bacteria that causes the plague inside teeth taken 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 strains of plague circulating today.

“What we find in this cemetery … was the ancestor of four of those five lineages – so it’s really like the big bang of the plague,” Johannes Krause, a professor at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, told a news conference. of press. “So we basically located this origin in time and space, which is really remarkable.”

Krause and several coauthors published their findings in the journal Nature.

Yersinia pestis bacterium (NIAID/Universal Images Group via Getty Images)

Yersinia pestis bacterium (NIAID/Universal Images Group via Getty Images)

The findings remove some assumptions from the story, help researchers better understand how the plague pandemic spread across the world, and tell more about the conditions that allowed the Black Death to emerge. The research also highlights rapid improvements in DNA sequencing, which can help scientists study patterns of other historic diseases — and prepare for future outbreaks.

Some historians have long suspected that examined burial sites in Kyrgyzstan contained plague victims. Now, there is physical proof.

“This is concrete evidence that these people, who were previously suspected of having died of the plague, are known for certain to have died during the early stages of the Black Death,” said Sharon DeWitte, a bioarchaeologist and professor at the University of South Carolina. . , who has studied the Black Death for two decades, but was not part of this research. “I am convinced by the findings.”

The pandemic swept Europe in the 1340s with a reputation that predated its onslaught.

In London, people set aside land for a cemetery before the plague reached the city.

After hearing reports elsewhere in Europe, “they knew it was inevitable that the plague would come and many people would die,” DeWitte said.

Most cities have lost between 30% and 60% of their populations during widespread outbreaks, she said. The disease was caused by a bacterium that would later become known as Yersinia pestis.

There are several theories as to how the bacteria spread in the 14th century. The most popular theory is that it was spread by fleas that accompanied black rats, which sometimes hitchhiked to new places with traveling humans. Another theory blames human fleas and 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.

Excavation of the KaraDjigach site in the Chu Valley of Kyrgyzstan, at the foot of the Tian Shan Mountains, August 1886. This excavation was carried out between the years 1885 and 1892. (AS Leybin)

Excavation of the KaraDjigach site in the Chu Valley of Kyrgyzstan, at the foot of the Tian Shan Mountains, August 1886. This excavation was carried out between the years 1885 and 1892. (AS Leybin)

For centuries, cities continued to resist outbreaks. Researchers disagree 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 struck several other cities later.

Burial sites in present-day Kyrgyzstan, where excavations began in 1885, have piqued researchers’ curiosity for years. The sites, two Christian cemeteries, featured 467 tombstones that are nearly 900 years old, according to Philip Slavin, author of the paper and an associate professor of history at the University of Stirling in the UK.

Some 118 of these headstones were from 1338 and 1339, including some with inscriptions marked “pestilence”, but it was unclear exactly what this meant.

“Obviously, when you have a year or two with excess mortality, that means something funny is happening there,” Slavin said at a recent press conference. “And 1339 is just seven or eight years before the Black Death hits Europe.”

Plague inscription from the Chu Valley region of Kyrgyzstan, August 1886. The inscription is translated as follows: “In the year 1649 [= 1338 CE], and it was the year of the tiger.  This is the tomb of the Sanmaq believer. [He] died of plague.

Plague inscription from the Chu Valley region of Kyrgyzstan, August 1886. The inscription is translated as follows: “In the year 1649 [= 1338 CE], and it was the year of the tiger. This is the tomb of the Sanmaq believer. [He] died of plague.

The research team extracted seven teeth from seven people buried in cemeteries during 1338 and 1339. The pulp of ancient teeth is filled with dried blood vessels and is most likely to contain evidence of blood-borne pathogens such as the bacteria that caused the Black Death. .

The researchers sequenced all of the old, degraded DNA found inside the teeth and pieced together disparate strands, which provided evidence of the bacteria’s presence.

So “we were able to target the entire genome and reconstruct the entire genome of 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 about eight years later.

They also found that marmots living today in the Tian Shan 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 quickly spread in the community where the cemeteries were located. The community — which is near Lake Issyk-Kul in present-day Kyrgyzstan — had around 1,000 people living there before the disease struck, according to Slavin.

It was a trading post along the Silk Road, with people of many ethnicities and origins. Trade and travel likely sent the plague to other regions.

Spyrou said that determining where the Black Death originated gives researchers a basis for 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 may open doors to understanding other historical disease outbreaks.

“To be able to analyze the entire genome of the strain that existed 700 years ago — it’s extraordinary,” said DeWitte. “People are excited to look at other diseases from the past.”

Plague remains a concern today, particularly in rural areas. It can be treated with antibiotics. Improvements in hygiene have greatly reduced transmission.

Still, some countries have faced major outbreaks. Madagascar in 2017 reported more than 2,400 cases of pneumonic plague, which can be spread through the air.

Krause said Black Death research — and the world’s experience of the coronavirus pandemic — calls for more emphasis on understanding what diseases animals are harboring that could spread to humans.

The animal overflow that caused the Black Death bears some resemblance to the diseases that are making headlines today.

“We really have to step up our efforts to understand the diversity of pathogens in animal reservoirs – to monitor them,” Krause said.

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