Quirks and Quarks

The Black Death was history's most lethal plague. Now scientists say they know where it started

Gravestones in a cemetery in Kyrgyzstan, several years before the plague broke out in Eurasia and Africa, identified people who died of a "pestilence." Their remains preserved microbial DNA from the bacteria that bore the genetic fingerprint of the Black Death.

Ancient DNA has identified the earliest victims of the Black Plague in Kyrgyzstan in central Asia

The headstone of the believer Sanmaq, from a graveyard in the Lake Issyk-Kul region of present-day Kyrgyzstan. The epitaph on his headstone, written in Syriac, reads: 'In the Year 1649 (AD 1337–8), died of pestilence (mawtānā).' This photo was taken during the original excavations in the late 19th century. (A.S. Leybin)

There are few events in human history as ominous — both in name and impact — as the Black Death.

The bubonic plague pandemic made its way across Eurasia and north Africa between 1346 and 1553. It's estimated to have killed up to 200 million people, or 60 per cent of the Earth's entire population at the time.

Now, scientists believe they have pinpointed the origin of the Black Death to a region of present day Kyrgyzstan called Issyk-Kul, once a stopover on the Silk Road trade route in the 14th century. 

Its place of origin has been one of the most hotly debated controversies in the history of epidemiology. Philip Slavin, an associate professor of environmental history at Stirling University in Scotland, and part of the research team, told Quirks & Quarks host Bob McDonald there have been a couple of prevailing theories over the past 200 years. 

"The Black Death was thought to have originated either in China or in Central Asia," Slavin said. "But one thing in common to those theories was that there was absolutely no way to actually prove those theories without the ancient DNA."

An old picture of people digging in a grassy plain in front of a mountain range.
In the late 19th century, archeologists excavated this cemetery in the Chu-Valley of Kyrgyzstan within the foothills of the Tian Shan mountains. (A.S. Leybin)

14th century grave markers referred to 'pestilence'

The new study began several years ago when by chance Slavin came across a graveyard in the Lake Issyk-Kul region of present-day Kyrgyzstan. The graveyard had clearly marked and dated gravestones that showed an unusually high number of burials in the years 1338 and 1339.

"What's really remarkable is that some of those tombstones, the inscriptions were actually longer and more detailed than others," Slavin said. "They stated very precisely that the cause of the death of those individuals was 'pestilence.'" 

Slavin wanted to investigate further, because these deaths occurred only six or seven years before the Black Death turned up in Europe. He thought there could be a connection. So he and his colleagues looked for ancient DNA from skulls that had been found by archeologists from the graveyard during excavations in the 1880s and 90s.

An oval stone engraved with a cross and other markings.
A gravestone from the medieval cemetery in Kyrgyzstan. Researchers found stones like this with engravings identifying victims of 'pestilence' from 1338 and 1339. (Pier-Giorgio Borbone)

Microbial DNA from the skulls matched DNA from the plague bacterium called Yersinia pestis, the strain responsible for the plague.

Their research was published in the journal Nature.

"We also were able to actually compare that strain to other strains from the Black Death in Europe. And what we found, astonishingly, is that genetically, that particular strain from northern Kyrgyzstan actually precedes the other strains from Europe." Slavin said.

"It is situated exactly just before a very important evolutionary event," which Slavin and his colleagues came to call the plague bacteria's "big bang" of diversification into different genetic variants. "So that strain preceded this huge big bang, whereas the main line split into four new lines. And one of those lines actually gave birth to the Black Death in Europe. So we know it actually started there in Central Asia."

A painting in medieval style.
The medieval bubonic plague outbreak known as the Black Death may have killed up to 200 million people. This miniature by Pierart dou Tielt (c. 1353) illustrates the people of Tournai in Belgium burying plague victims. (Pierart dou Tielt )

The value of ancient DNA 

Dr. David Fisman, an epidemiologist at the University of Toronto, said in an email that ancient DNA studies like this "have really provided a lot of insights into the origins of historical plagues."

In particular, he pointed to the value of the nucleic amplification technology that the researchers used, which allowed them to take tiny amounts of preserved ancient DNA and make copies of it to study.

"The ability to amplify sequences, even when material has been buried in the ground for centuries, does transform the way we understand epidemics." 

But in the case of understanding where the Black Death originated, ancient DNA answered only one part of the mystery. Slavin and his team still didn't know how this virulent strain of plague got into humans in the first place. 

The bubonic plague often persists in the wild in rodents, and Slavin thinks he knows which species was responsible.

"It was really bound to start with local marmots, because the marmot is the most prevalent type of plague-carrying rodent in that region." Salvin said. Marmots are large ground squirrels common in the area.

"And at some point, something must have happened which prompted those bacteria to cross over from marmots into humans. Usually what happens is that you have population collapse in those rodents. And then fleas which are carrying the bacteria become very, very unhappy, and they start seeking an alternative host — and this [new host] is usually humans." 

A mountain range with grassland fields in the foreground.
The Tian Shan mountains, where researchers traced the origins of the Black Death close to Lake Issyk Kul, in what is now Kyrgyzstan. (Lyazzat Musralina)

The Black Death takes the Silk Road

Another key part of the story is that this region of Kyrgyzstan was a stopover on the Silk Road trading route that extended from China to western Europe. The Black Death then spread by humans, or fleas travelling with humans, as they travelled the Silk Road, according to Slavin.

"We suspect that both long-distance trade and the local regional trade were a very, very paramount factor in spreading this disease all the way from Tian Shan region into west Eurasia and beyond," he said.

Written and produced by Mark Crawley