According to archaeogeneticist Maria Spyrou of Eberhard Karls University of Tübingen in Germany and colleagues, a strain of the plague-causing Yersinia pestis bacterium that killed people in what is now Kyrgyzstan in 1338 and 1339 was a common ancestor of four Y. pestis strains previously linked to the deadly European outbreak. Although best known as a plague that killed millions of Europeans from 1346 to 1353, a new study suggests that the Black Death began about a decade earlier in Central Asia.
Spyrou’s team discovered Y. pestis DNA in the teeth of three people from an ancient Central Asian cemetery where tombstone inscriptions state that they, along with many others buried there, died in 1338 and 1339 from an unspecified “pestilence.” Comparisons of that genetic material to modern and historic samples of Y. pestis DNA show that the Central Asians died from an early version of the plague bacterium that would wreak havoc on Europe, the Middle East, and northern Africa until the early 1800s, the scientists report in Nature.
“The source location and time when this plague emerged was most likely in Central Asia in the first half of the 14th century,” Spyrou said in a news briefing.
The origins of the Black Death, also known as the bubonic plague, have long been debated. What is certain is that fleas that live on rodents transmit Y. pestis to humans. According to one current theory, the plague bacterium originated in East Asia and spread across the continent beginning in the 1200s as the Mongol Empire expanded. That theory was based on genetic evidence from European Black Death victims as well as written accounts of an unknown plague outbreak encountered by Mongol invaders of Baghdad in the 1200s.
The source location and time when this plague emerged was most likely in Central Asia in the first half of the 14th century. The causes of the rise of a particularly lethal strain of Yersinia pestis in Central Asia in the early 1300s are unknown.
Maria Spyrou
However, the first archaeological and genetic clues to the location and timing of the Black Death come from Central Asia, according to Spyrou. Excavations in two cemeteries in northern Kyrgyzstan nearly 140 years ago revealed tombstones indicating that many people buried there in 1338 and 1339 died as a result of an unknown epidemic. The cemeteries were used from the mid-1200s to the mid-1300s, but tombstone inscriptions show that deaths increased in 1338 and 1339. In those two years, 118 people died, according to the 467 dated tombstones.
Spyrou’s group was able to reconstruct the entire Y. pestis genome for two of three Central Asian individuals who died in 1338 or 1339 and whose teeth contained remnants of bacterial DNA. Comparisons with the genetic instructions of 203 modern Y. pestis samples and 47 Y. pestis samples dating from the 14th to 19th centuries pegged the Central Asian genomes as a single strain that was a direct ancestor of Black Death strains.
The researchers also discovered that marmots and other rodents living in the same region of Central Asia now carry Y. pestis strains that are closely related to the ancient variant. According to the researchers, the Y. pestis variant that killed Central Asians in 1338 and 1339 may have emerged locally.
The causes of the rise of a particularly lethal strain of Yersinia pestis in Central Asia in the early 1300s are unknown. The earliest known Y. pestis strain, which lived around 7,100 years ago in Eastern Europe, lacked a plague-inducing gene that allows fleas to transmit disease to humans quickly.
According to evolutionary biologist Nils Stenseth of the University of Oslo, who did not participate in the study, Spyrou’s group convincingly traces the origin of Y. pestis strains involved in Europe’s Black Death to Central Asia. He believes the new findings support a scenario in which warm weather in Central Asia triggered repeated plague outbreaks in Europe beginning in the 1300s. Stenseth suspects that troops, travelers, and merchants traveling along trade routes from Asia continued to bring the plague into Europe.
While the newly identified Y. pestis strain appears to be an ancestor of later European strains, the origins of the Black Death — and other pandemics such as COVID-19 — are notoriously difficult to pinpoint, according to evolutionary geneticist Hendrik Poinar of McMaster University in Hamilton, Canada.
For example, determining whether the ancient Y. pestis strain from Central Asia existed even earlier across a large swath of the continent will be difficult, he says. If this is the case, a precursor strain of the Black Death may have emerged prior to 1338 in an as-yet-unidentified region of Asia. Temptations to turn ancient DNA discoveries into a story of the Black Death’s precise location and time of origin “need to be tempered,” he says.
