Where did the Black Death begin? DNA detectives find a key clue

Where and when did the Black Death originate? The question has been asked for centuries and led to heated debate among historians.

Now, a group of researchers reports that it has found the answer in the pulp of teeth from people buried in the 14th century.

Based on their analysis of the preserved genetic material, the researchers report that the Black Death arrived in 1338 or 1339 near Issyk-Kul, a lake in a mountainous area just west of China in what is now Kyrgyzstan. The plague first infected people in a small, nearby settlement of traders eight years before it devastated Eurasia, killing 60% of the population.

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

What was known as the Black Death — named after black spots that appeared on victims’ bodies — is caused by a bacterium, Yersinia pestis, that is carried by fleas that live on rodents. The disease is still present 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 large Yersinia pestis epidemic — the first was the Plague of Justinian in the sixth century, said Mary Fissell, a medical historian at Johns Hopkins University. But the Black Death is the best known and is considered one of the deadliest epidemics in human history.

Its terrors were chronicled by Giovanni Boccaccio, an Italian writer and poet who lived through the plague when it struck Florence. The disease, he wrote, “showed its first signs in men and women alike by means of swellings either in the groin or under the armpits, some of which grew to the size of an ordinary apple and others to the size of an egg, and the people called them buboes,” which became known as “signs of impending death.”

Historians traced the epidemic’s path — it apparently began in China or near the western border of China and moved along trade routes to Europe, North Africa and the Middle East.

But Monica Green, a medical historian and independent scholar who was not involved in the new paper, noted that historians would never be able to answer the question they raised: Was it really Yersinia pestis that caused this massive pandemic?

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

She vividly remembers meeting a paleopathologist 20 years ago who had been studying leprosy, which leaves visible marks on skeletons.

“When will you do plague?” Green asked. She said the paleopathologist replied that they couldn’t study plague because a disease that kills people so quickly does not leave any traces on bone.

Now that impasse has been overcome.

The search for the plague’s origin “is like a detective story,” said Fissell, who was not involved in the new study. “Now they have really good evidence of the scene of the crime.”

The hunt goes back more than a decade, to when the group that led the latest study stunned archaeologists with their report that they could find plague bacteria DNA in the teeth of skeletons.

That study involved plague victims in London.

Fourteenth-century Londoners knew the Black Death was coming, so they consecrated a graveyard in advance to be prepared for its victims. The bodies were exhumed and are now kept in the Museum of London. The situation was ideal because not only were these victims from a plague graveyard, but the date of their death was known.

“As an epidemiological case study, it is perfect,” Green said. “The technical skill that has gone into this work has just been amazing.”

Since the London study, the group has analyzed genetic material from plague victims at other sites, building a DNA family tree of the plague bacteria variants. It and other researchers reported that the tree had a trunk and then, all at once, seemed to explode into four branches of Yersinia pestis strains whose descendants are found today in rodents. They called the event the Big Bang and began a quest to find when and where it occurred.

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

Slavin, a latecomer to the group that analyzed plague victims in Kyrgyzstan, said one of his dreams was to solve the riddle of the Black Death’s origins.

“I was aware of two Christian cemeteries in Kyrgyzstan and started delving,” he said.

To his astonished delight, he found that hundreds of gravestones were precisely dated. Some had inscriptions saying, in an old language, Syriac, that the person had died of “pestilence.” And the population’s death rate had soared in the year those people died.

“That brought it to my attention because it wasn’t just any year,” Slavin said. It was 1338, “just seven or eight years before the Black Death came to Europe.”

“We can’t ask for much more than having tombstones with the year,” he said.

The researchers found plague DNA in the teeth of three individuals whose tombstones said had they died of “pestilence.”

The group also reports that the rodents that spread the bacteria to those victims were marmots. Marmots in that area today have fleas that carry a type of Yersinia pestis that appears to be derived directly from the ancestral strain.

And the researchers report that the strain in Kyrgyzstan is from the trunk that exploded into four strains. It is the start of the Big Bang, the group proposes.

If they are correct, Fissell said, it seems that the Big Bang happened right before the Black Death in Eurasia, indicating that the plague’s spread was most likely through trade routes and not, as some historians have suggested, through military actions a century earlier.

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

“Those battles in the 1200s are pretty irrelevant,” Fissell said.

Green said she was convinced that the group had found plague victims in Kyrgyzstan. But she said the evidence available now was insufficient to justify its bold claims.

“Stay tuned,” Green said, adding she expected that more evidence might emerge.

For now, she said, the detective work has nailed down an important clue.

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

[This article originally appeared in The New York Times.]