It was thanks to ancient human DNA, extracted from a 14th century burial site in northern Kyrgyzstan, that researchers were able to trace the source.

Their findings, published Wednesday in the journal Nature, settle a very old debate among historians.

The Black Death epidemic reached Europe in 1346 through the Mediterranean basin, via ships carrying goods from the Black Sea.

In just eight years, the "black death" killed up to 60% of the population of Europe, the Middle East and North Africa.

And marked the beginning of a long wave of the epidemic, which would resurface intermittently for 500 years.

Where was she born ?

One of the most commonly advanced leads was that of China, but no robust evidence could support this theory.

"I have always been fascinated by the Black Death, and one of my dreams was to solve the mystery of its origins," said disaster historian Phil Slavin, one of the study's authors. during a press conference.

"Death of Pestilence"

This professor at the University of Stirling (Scotland) knew of the existence of two medieval burial sites near Lake Issyk Kul in Kyrgyzstan, which had been excavated at the end of the 19th century.

Of more than 400 tombstones, a hundred were precisely dated: 1338-1339.

With an epitaph mentioning an elliptical "death of pestilence", in Old Syriac.

So many signs of abnormal excess mortality within a community, seven or eight years before the Black Death hit Europe.

At the foot of the mountains in the Tian Shan, where the Black Death pandemic that raged in the Middle Ages originated, photo taken in 1886 during excavations and transmitted by Nature on June 14, 2022 AS Leybin HANDOUT / AFP

To find the cause of death, the researchers searched through the dental DNA of seven skeletons.

"The dental pulp is a valuable source, because it is a highly vascularized area which gives a high chance of detecting pathogens in the blood," Maria Spyrou, from the University of Tübingen in Germany, told AFP. also author of the study.

The DNA could be sequenced – a delicate job as it was fragmented – and then compared to a database containing the genome of thousands of bacteria.

Verdict: the bodies had been infected with the bacterium Yersinia pestis, the bacillus responsible for the black plague, transmitted to humans by rodent fleas.

This community had therefore been the victim of the same scourge that struck Europe a few years later.

Analyzes of the genome of Yersinia pestis also revealed that it was an ancestral strain of the bacterium.

The one that is at the base of the "genetic tree" of the plague.

Scientists rightly associate the appearance of the Black Death in Europe with a genetic "Big Bang" during which the stem bacteria massively diversified.

In the heart of the Silk Roads

The strains discovered in Kyrgyzstan are right "at the crux of this massive diversification", which occurred around the 1330s. Confirming that this region of the world, the Tian Shan, was indeed the starting point of the expansion, according to Maria Spyrou.

In addition, in rodents living today in the Tian Shan, the researchers identified a strain of the bacterium very close to that of the human victims of 1338-1339, "the closest that has been found in the world", added Johannes Krause, of the Max Planck Institute, co-author of the study.

These were Christian communities, ethnically diversified (Mongols, Uyghurs...), who practiced long-term trade according to the funerary objects found: pearls from the Pacific, corals from the Mediterranean, silk clothes... "Living in the heart of the Silk Roads, they had to travel a lot, which played a role in the expansion of the epidemic via the Black Sea”, says Phil Slavin.

The plague has never been eradicated from the face of the Earth: every year thousands of people continue to be infected, especially in Central Asia.

In the Tian Shan Mountains, marmots are the main animal reservoir of the disease.

A deadly pandemic like that of the Middle Ages is fortunately not to be feared: not that the bacterium is less virulent, but because the conditions of hygiene and the use of antibiotics have nothing to do with the past.

© 2022 AFP