Where did the Black Death begin? DNA detectives find key clues.

Where and when did the Black Death originate? This question has been asked for centuries and sparked a heated debate among historians.

Now, a team of researchers reports that it found the answer in the pulp of people buried in the 14th century.

Based on their analysis of preserved genetic material, the researchers report that the Black Death arrived in 1338 or 1339 near Lake Issyk-Kul, a lake in the mountains of western China in what is now Kyrgyzstan. The plague, which first infected people in a small nearby settlement of traders, devastated Eurasia eight years ago, killing 60 percent of its victims.

The investigation, led by Wolfgang Haak and Johannes Krause of the Max Planck Institute for the Science of Evolutionary Anthropology and Human History in Germany, and Philip Slavin of the University of Stirling in Scotland, described their findings in the journal Nature on Wednesday.

The so-called Black Death — named for the black spots that appeared on victims — was caused by Yersinia pestis, a bacterium carried by fleas on rodents. The disease still exists today, carried by rodents on every continent except Australia. But infections are rare because hygiene is better. Infections are easily cured with antibiotics.

The 14th-century plague was actually the second major plague epidemic—the first was the sixth-century plague of Justinian, says Mary Fissel, a medical historian at Johns Hopkins University. But the Black Death is the most famous, considered one of the deadliest epidemics in human history.

Its horrors were recorded by Italian writer and poet Giovanni Boccaccio, who experienced the plague when it struck Florence. He wrote that the disease “shows its first signs in both men and women through swelling in the groin or under the armpit, some of which grow to the size of an ordinary apple, others the size of an egg, And people call them “swollen groin,” which are called “signs of imminent death.”

Historians trace the path of the epidemic – it apparently started in China or near the western border of China and spread along trade routes to Europe, North Africa and the Middle East.

But medical historian and independent scholar Monica H. Green, who was not involved in the new paper, points out that historians will never be able to answer the question they ask: Yersinia pestis really caused the pandemic sick?

“We hit a wall. We are historians and we deal with documents,” Dr Green said.

She vividly remembers meeting a paleopathologist 20 years ago who was studying leprosy, which had left visible marks on the bones.

“When did you do the plague?” Dr. Green asked. She said paleopathologists responded that they could not study the plague because the disease, which kills people quickly, leaves no marks on the bones.

Now this deadlock has been broken.

Finding the origins of the plague “was like a detective story,” said Dr. Feisel, who was not involved in the new study. “Now they have very good crime scene evidence.”

The hunt dates back more than a decade, when the team leading the latest study shocked archaeologists with reports that they could find plague bacteria DNA in the teeth of skeletons.

The study involved plague victims in London.

14th century Londoners knew the Black Death was coming, so they dedicated a cemetery in advance to prepare for the victims. The bodies were exhumed and are now kept in the London Museum. This situation is ideal because not only are these victims from the plague cemetery, but the dates of their deaths are also known.

“As an epidemiological case study, it’s perfect,” Dr. Green said.

“The technical skills for the job are amazing,” she added.

Since the London study, the team has analysed the genetic material of plague victims at other sites, building a DNA family tree of variants of the plague bacterium. It and other researchers reported that the tree had a trunk and then appeared to explode into four strains of Yersinia pestis in one fell swoop, descendants of which are found in rodents today. They dubbed the event the Big Bang and set out to find when and where it occurred.

Historians have proposed various dates from the 10th to the 14th century.

Dr Slavin, a latecomer to the group analyzing the victims of the plague in Kyrgyzstan, said one of his dreams was to solve the mystery of the origins of the Black Death.

“I knew there were two Christian cemeteries in Kyrgyzstan and started to delve into it,” he said.

To his surprise, he found hundreds of gravestones to be dated accurately. Some have inscriptions in Syriac, an ancient language, that the man died of the “plague”. In the year these people died, the death rate of the population soared.

“This caught my attention because it’s not just any year,” Dr. Slavin said. It was 1338, “only seven or eight years before the Black Death was introduced to Europe”.

“We can’t ask for more than we had tombstones back then,” he said.

Researchers have found plague DNA in the teeth of three people whose tombstones say they died of “the plague.”

The team also reported that the rodents that transmitted the bacteria to these victims were woodchucks. Today, fleas on groundhogs in the area carry a strain of Yersinia pestis that appears to be derived directly from an ancestral strain.

The Kyrgyz strain came from tree trunks that exploded into four strains, the researchers report. The team proposes that this is the beginning of the Big Bang.

If they are correct, the Big Bang appears to have occurred just before the Black Death in Eurasia, suggesting that the spread of the plague was most likely via trade routes, rather than as some historians have suggested, Dr Fiesel said. That way, through a century of military action earlier.

Dr. Green and other historians have proposed that the Big Bang occurred when the Mongols spread the bacteria in the early 13th century. But if that were the case, the bacteria in Kyrgyzstan would have come from one of these branches, not the ancestral strain.

“Those battles in the 1200s were completely irrelevant,” Dr. Feisel said.

Dr Green said she was sure the group had found plague victims in Kyrgyzstan. But she said the evidence now available was insufficient to justify her bold claims.

“Stay tuned,” Dr. Feisel said, adding that she expected more evidence could emerge.

For now, detective work has identified an important lead, she said.

The work, she added, “puts a pin on the map with a date on it.”

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