By Will Dunham
(Reuters) – Ancient DNA from bubonic plague victims buried in cemeteries along the ancient Silk Road trade route in Central Asia has helped solve an ongoing mystery, identifying an area in northern Kyrgyzstan as the starting point for the Black Death that killed tens of millions took the lives of people in the mid-14th century.
Researchers said on Wednesday they had found ancient DNA traces of the plague bacterium Yersinia pestis from the teeth of three women living in a medieval Nestorian Christian community in the Chu Valley near Lake Issyk-Kul in the foothills of the Tian Shan Mountains were buried and died in 1338-1339. The earliest deaths documented elsewhere in the pandemic were 1,346.
Reconstruction of the pathogen’s genome showed that this strain gave rise not only to the one that caused the Black Death that afflicted Europe, Asia, the Middle East and North Africa, but also to most of the plague strains in existence today.
“Our finding that the Black Death originated in Central Asia in the 1330s puts an end to centuries-old debates,” said historian Philip Slavin of the University of Stirling in Scotland, co-author of the study published in the journal Nature. www.nature.com/articles/s41586-022-04800-3.
The Silk Road was an overland route for caravans that carried a plethora of goods from China through the magnificent cities of Central Asia to places like the Byzantine capital of Constantinople and Persia. It could also have served as a death channel if the pathogen went with the caravan.
“There have been a number of different hypotheses suggesting that the pandemic could have originated in East Asia, specifically China, in Central Asia, in India or even near where the first outbreaks occurred in 1346 in the regions of the Black Sea and the Caspian Sea have been documented,” said archaeogeneticist and lead author of the study Maria Spyrou of the University of Tübingen in Germany.
“We know that trade at the onset of the Black Death was likely a key factor in the spread of the plague across Europe. It is reasonable to assume that similar processes determined the spread of the disease from Central Asia to the Black Sea between 1338 and 1346,” Spyrou added.
The origins of pandemics are hotly debated, as illustrated by the debate surrounding the emergence of the current COVID-19 pandemic.
The Black Death was the deadliest pandemic of all time. It could have killed 50 to 60 percent of the population in parts of western Europe and 50 percent in the Middle East, totaling about 50 to 60 million deaths, Slavin said. An “unexplainable number” of people also died in the Caucasus, Iran and Central Asia, Slavin added.
“As early as the Middle Ages, we see the high mobility and rapid spread of a human pathogen,” said archaeogeneticist and study co-author Johannes Krause, director of the Max Planck Institute for the Science of Human History in Germany. “We shouldn’t underestimate the potential for pathogens to spread from fairly remote locations around the world, likely due to a zoonotic event” — an infectious disease that jumps from animals to humans.
Researchers analyzed teeth, a rich source of DNA, from seven people buried in cemeteries of communities named Burana and Kara-Djigach, and obtained plague DNA from three in Kara-Djigach.
The cemeteries excavated in the 19th century contained tombstones attributing deaths to the “plague” in the Syriac language. Items such as beads, coins, and clothing from distant locations indicated that the cities were involved in international trade and might have provided stopping places for long-distance caravans.
The bubonic plague, then untreatable but now curable with antibiotics, caused swollen lymph nodes, oozing blood and pus, and the infection spread to the blood and lungs.
In Europe, it was mainly transmitted through bites from fleas carried by infected rats. The pandemic originated in wild rodents, most likely marmots, a type of ground squirrel, Slavin said. Rodents traveling in trailers may have contributed to the spread, but other transmission mechanisms may have included human fleas and lice.
“We found that the closest living relatives of this Y. pestis strain that caused the Black Death can still be found in marmots in this region today,” Krause said.
(Reporting by Will Dunham in Washington, Editing by Rosalba O’Brien)