Unlocking the 700-year-old mystery of the origin of the Black Death

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2022-07-25 19:28:40

Now, researchers claim to have found the genetic ancestor of the Black Death, and it still infects thousands of people each year. New research published in the journal Nature last month (June 2022) provides biological evidence that pinpoints the location of the Black Death as in Central Asia, present-day Kurgyzstan.

In addition, the plague strain inherited from this region “has given rise to most strains [dịch hạch hiện đại] spread in today’s world”historian Phil Slavin at the University of Stirling (Scotland), study co-author said on NPR.

Like many other mysteries, solving this mystery is not easy at all.

Old clues

The Black Death was one of many strains of plague. The disease is given this scary name because those infected will have sores all over the body, the sores will darken and cause necrosis. The disease is characterized by flu and swollen lymph nodes. The cause of the disease is the bacterium Yersinia pestis, which is spread by rats carrying the disease-causing fleas.

In the past, a single plague strain evolved into four different strains. One of these strains caused the Black Death. Just how and where the epidemic occurred is a mystery, the researchers say.

Plague researchers worldwide have long suspected that the evolution of the bacterium Yersinia pestis may have occurred in the Tianshan Mountains near the Chuy Valley (the Kyrgyz word is Chüy) on the border. Northern Kyrgyzstan. The area was on the Silk Road, a famous medieval trade route from China and Central Asia to Western Europe.

A view of Thien Son mountain in northern Kyrgyzstan, where scientists believe the origin of the Black Death epidemic disaster (Photo: Reuters)

This clue was discovered by researchers in 1885, when they discovered two cemeteries in the area with unusually high number of gravestones with dates of death from 1338 to 1339. 1338-1339 was about 8 years before the Black Death epidemic began in Europe.

These tombstones also refer to the cause of death as mawtānā, a Syriac word for plague. It was an indication that the disease may have swept the area, and also motivated Slavin and his colleagues to dig deeper. However, the researchers say that, while the evidence of the tombstones is quite convincing, they are not enough to prove that the people there really died from the plague. Historian Slavin and his team needed genetic evidence.

Ancient DNA test

So the team turned to ancient DNA experts for help. DNA was extracted from corpses associated with two cemeteries, said geneticist Maria Spyrou of the University of Tübingen (Germany), lead author of the study. Hundreds of bodies were removed from these cemeteries during excavations between 1885 and 1892 and transferred to the Kunstkamera, the anthropological and ethnographic museum of Peter the Great in St. Petersburg (Russia).

Spyrou and his colleagues took tooth samples from seven stored cadavers. Teeth have many blood vessels, so they are the most likely place to find evidence of a blood-borne disease, as long as the rest of the body is indeed destroyed.

Using DNA sequencing, the team recovered traces of Yersinia pestis DNA in three tooth samples. In other words, the researchers can confirm that the people in the Chuy valley died from the disease.

Monitor disease strains

The scientists’ next work is to see how closely the Chuy valley plague strain is related to the Black Death and other plague strains.

To accomplish this task, the team sequenced the DNA of modern plague-causing strains (from ground squirrels and other Central Asian rodents) and historical plague-causing strains such as the Black Death ( from previously published studies). The scientists used these sequences to create an evolutionary tree that reflected the relationships between plague strains and compared them with the Chuy valley disease strain.

This evolutionary tree revealed that the strain in the Chuy valley differed only from the strain that caused the Black Death in two genetic mutations. The Chuy valley strain was older than the Black Death, so the researchers concluded that the Black Death evolved from the Chuy valley. In addition, the evolutionary tree also revealed that the Chuy valley plague strain was the ancestor of most of the plague strains in the world. From this “ancestor” of the plague, bubonic plague evolved into four main strains, and this event was called the “Big Bang” by researchers. Until now, scientists still do not know where and when the “Big Bang” originated. But now they have evidence that it may have come from the Chuy valley and surrounding areas.

Does all this mean that the mystery of the Black Death’s origins has been solved?

One scientist who was not involved in this study, Hendrik Poinar, an evolutionary geneticist and director of the Center for Ancient DNA at McMaster University in Ontario (Canada), said he would be very cautious about taking the matter too far. so. “It is not accurate to determine a specific date and location in an instant”.

He explained, the bacterium Yersinia pestis evolves very slowly, only having a mutation every 5 to 10 years. So it is possible that the strain in Chuy valley came from another part of the region.

In addition, the people of the Chuy valley were merchants who moved throughout Central Asia and Europe. It is possible that they contracted the disease during their travels to Western Europe. Because this strain is slow to mutate, the Western European strain is genetically identical to the Chuy valley strain, so it is difficult to say where and when it came from.

Still, Poinar says the work is important in understanding the early history of the Black Death because it helps us answer questions that plague researchers have spent years figuring out. Now we know that, “the bubonic plague was there 10 years ago when strains of the disease raged in Western Europe, and I think that’s an important piece of the bubonic puzzle.”.

Refer to NPR

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