Black Death: DNA analysis reveals source of plague

Black Death: DNA analysis reveals source of plague

The source of this pandemic has been debated by historians for centuries, but the inscribed headstones – some of which referred to a mysterious plague – and genetic material from bodies exhumed from two burial sites from the 13th century have provided concrete answers to this long-standing question.

Researchers first excavated the burial sites in the 1880s. The tombstone inscriptions, written in Syriac, were carefully reviewed in 2017 by historian Phil Slavin, an associate professor at the University of Stirling in Scotland. He noted that of the 467 burials that were accurately dated, a disproportionate number—118—were from just two years: 1338 and 1339. It’s a revelation he called “amazing.”

“If you have a year or two of excess mortality, it means something was going on. But another thing that really caught my attention is the fact that it wasn’t just any year – because it was only seven or eight years before the war (plague) actually came to Europe,” Slavin said in a press conference.

“I’ve always been fascinated by the Black Death. And one of my dreams was to actually be able to solve this mystery of his origins,” he added.

Slavin and his associates discovered that the remains of 30 of those buried in the tombs of Kyrgyzstan had been moved to Peter the Great’s Anthropological Museum Ethnography in St. Petersburg, Russia. The research team was able to get permission to extract DNA from the skeletons to understand how they died.

In seven of the people, the researchers were able to extract and sequence DNA from their teeth. In this genetic material they found the DNA of the plague bacterium – which scientists call Yersinia pestis – in three of the people, all of whom had the year of death 1338 on their tombstones.

This confirmed that the plague mentioned on the tombstones was in fact the plague transmitted from rodents to humans via fleas.

In 1347, the plague first entered the Mediterranean via merchant ships transporting goods from areas around the Black Sea. The disease then spread across Europe, the Middle East and North Africa, claiming up to 60% of the population, according to the study published in the journal Nature on Wednesday.

Some historians believe the plague that caused the Black Death originated in China, while others believe it originated near the Caspian Sea. India was also mentioned as a possible source. The plague strain continued to circulate around the world for 500 years.

Shown is the original excavation of the Kara Djigakh Cemetery near Lake Issyk Kul in Kyrgyzstan.

Evolution of the plague strain

The latest study adds to a wealth of information uncovered by sequencing ancient pathogens like plague, which leave a genetic imprint in human DNA.

In 2011, scientists first sequenced the genome of the plague bacterium Yersina pestis, found in two plague victims buried in a pit in London. Since then, more genetic material has been recovered from burial sites across Europe and southern Russia.

This work showed a Explosion in the diversity of plague strains – a Big Bang – that occurred in the evolution of the plague bacterium sometime before the Black Death ravaged Europe – most likely in the 10th and 14th centuries.

The world's first known plague victim was a 5,000-year-old hunter-gatherer in Europe

Researchers involved in this latest study believe the area around the two cemeteries is near Lake Issyk-Kul in Kyrgyzstan must have been the origin of the plague strain that caused the Black Death, as two ancient plague genomes the team pieced together from the Teeth have revealed a single plague strain that is the most recent direct ancestor of this Big Bang event. This puts it at the very beginning of the Black Death outbreak and before it arrived in Europe.

“We found that the ancient tribes from Kyrgyzstan are positioned right at the nexus of this massive diversification event,” said the study’s lead author Maria Spyrou, a postdoctoral researcher at the University of Tübingen in Germany.

Further evidence to support the study researchers’ claim came from comparing plague strains found in modern rodents with those they had sequenced in the cemeteries. They found that the modern plague strains, which are most closely related to the ancient strain, are now found in wild rodents such as marmots living in the Tian Shan Mountains, very close to the two burial sites.

The epitaph on this tombstone is written in Syriac and reads: “This is the tomb of the believer Sanmaq. [He] died of the plague.”

“What is really remarkable is that today we have the closest living relatives of this big bang strain (of plague bacteria) in the rodents living in this region,” said lead study author Johannes Krause, director at the Max Planck Institute for Evolutionary Anthropology in Leipzig , Germany.

“Not only have we found the ancestor of the Black Death, but we have actually found the ancestor of most of the plague strains circulating in the world today.”

The team does not yet know a lot, for example from which animal exactly the disease jumped to humans. But understanding the origin of the largest pandemic in human history could help prepare for future disease transmissions, Krause said.

“Just like Covid, the Black Death was an emerging disease and the beginning of a huge pandemic that lasted about 500 years. It’s very important to understand the circumstances under which it actually occurred,” Krause said.