Where did the Black Death originally come from?

The Black Death, often known simply as the Plague, was a pandemic that ravaged North Africa and Eurasia between 1347-1351 where it is estimated to have killed up to 60% of the population.

The first wave then extended into a 500-year-long pandemic (termed the Second Plague Pandemic) which lasted until the early 19^th century and is considered one of the largest infectious disease catastrophes in human history.

It was caused by the Bubonic plague, a disease caused by the bacterium Yersinia Pestis, which is usually transmitted to humans via the parasitic fleas that feed upon infected rats. They first entered the Mediterranean in 1347 via trade ships transporting goods from the territories of the Golden Horde in the Black Sea.

The exact geographical origins of the plague have been long debated, but new ancient DNA analysis of individuals who died in the 14^th century suggests that the Black Death originated in communities in what is now modern-day Kyrgyzstan in the 1330s.

“Our study puts to rest one of the biggest and most fascinating questions in history and determines when and where the single most notorious and infamous killer of humans began,” says senior author Phil Slavin, associate professor of History at the University of Stirling, UK.

The research has been published in Nature.

The Black Death was inscribed on ancient headstones

Archaeological findings indicate that an epidemic devastated a local trading community close to Lake Issyk-Kul in the Chüy Valley of modern-day Kyrgyzstan, in the years 1338 and 1339.

Excavations almost 140 years ago revealed a disproportionally high number of burials and tombstones that indicated “pestilence” as the cause of death.

However, the relevance of these archaeological findings to the Black Death has remained controversial amongst experts until now.

An international team of researchers has now analysed ancient DNA (aDNA) from the teeth of the skeletal remains of seven individuals from this excavation and determined that DNA from Yersinia pestis was present in three that died there in 1338.

“Despite the risk of environmental contamination and no guarantee that the bacteria would have been able to be preserved, we were able to sequence aDNA taken from seven individuals unearthed from two of these cemeteries – Kara-Djigach and Burana in the Chu Valley. Most excitingly, we found aDNA of the plague bacterium in three individuals,” says lead author Dr Maria Spyrou, from the Institute for Archaeological Sciences at the University of Tübingen, Germany.

“We could finally show that the epidemic mentioned on the tombstones was indeed caused by plague,” adds Slavin.

Their archaeological and historical findings suggest that this area was the origin of the spread of the plague, as the ethnically diverse communities in the Chüy Valley relied on trade and maintained connections with several regions across Eurasia.

Origin of the Black Death is in Central Asia

The origins of the Black Death have been associated with a massive genomic diversification of Y. pestis strains, and though this was thought to have occurred sometime between the 10th and 14th centuries the exact date could not be estimated precisely.

However, using the ancient Y. pestis genome pieced together from the sites in Kyrgyzstan, the researchers have determined that this ancient strain must have been central to the diversification event.

“We found that the ancient strains from Kyrgyzstan are positioned exactly at the node of this massive diversification event. In other words, we found the Black Death’s source strain and we even know its exact date [the year 1338],” says Spyrou.

Plague still exists today, surviving within wild rodent populations around the world in plague reservoirs. The authors suggest that the ancient Central Asian strain that caused the 1338-1339 epidemic around Lake Issyk Kul must have come from one such reservoir.

“We found that modern strains most closely related to the ancient strain are today found in plague reservoirs around the Tian Shan mountains, so very close to where the ancient strain was found. This points to an origin of Black Death’s ancestor in Central Asia,” concludes senior author Johannes Krause, director at the Max Planck Institute for Evolutionary Anthropology, Germany.