Tombstones in what is now Kyrgyzstan have revealed compelling details about the origins of the Black Death, the world’s most devastating plague epidemic, which is thought to have killed half of Europe’s population in seven years in the Middle Ages.
The source of this pandemic has been debated by historians for centuries, but inscriptions – some of which refer to a mysterious plague – and genetic material from bodies exhumed from two 13th-century tombs have provided some concrete answers to this longstanding question.
Researchers first excavated burial sites in the 1880s. The tombstone inscriptions, written in Syriac, were thoroughly reviewed in 2017 by historian Phil Slavin, an associate professor at the University of Stirling in Scotland. He noted that of the 467 burials that are accurately dated, a disproportionately large number – 118 – are from just two years ago: 1338 and 1339. This is a revelation he described as “amazing”.
“When you have one or two years of excessive mortality, it means something has happened. But another thing that really caught my attention was the fact that it wasn’t a year – because it was only seven or eight years before (the plague) actually came to Europe, “Slavin told a briefing.
“I have always been fascinated by the Black Death. And one of my dreams was actually to be able to solve this mystery of its origin, “he added.
Slavin and his associates found that the remains of 30 of the people buried in Kyrgyzstan’s graves had been taken to the Peter the Great Museum of Anthropology and Ethnography in St. Petersburg, Russia. The research team was able to obtain permission to try to extract DNA from the skeletons to find out how they died.
For seven of the individuals, the researchers were able to extract and sequence DNA from their teeth. In this genetic material, they found DNA from the plague bacterium – which scientists call Yersinia pestis – in three of the individuals, all of whom had the year of death 1338 inscribed on their tombstones.
This confirmed that the plague mentioned on the tombstones was indeed the plague that was spread by rodents to humans through fleas.
In 1347, the plague first entered the Mediterranean through merchant ships carrying goods from around the Black Sea. The disease then spread to Europe, the Middle East and North Africa, taking up 60 percent of the population, according to a study published in the journal Nature on Wednesday.
Some historians believe that the plague that caused the Black Death originated in China, while others believe that it originated near the Caspian Sea. India has also been highlighted as a possible source. The plague strain has been circulating around the world for 500 years.
Evolution of the plague strain
The latest study adds to the abundance of information revealed by the sequencing of ancient pathogens such as plague, which leave a genetic imprint in human DNA.
In 2011, scientists for the first time sequenced the genome of the plague bacterium – Yersina pestis – found in two plague victims buried in a pit in London. Since then, more genetic material has been extracted from graves throughout Europe and southern Russia.
This work showed an explosion in a variety of plague strains – a big bang – that occurred in the evolution of the plague bacterium sometime before the Black Death ravaged Europe – most likely in the 10th and 14th centuries.
Researchers in this latest study believe that the area around the two cemeteries near Lake Issyk-Kul in Kyrgyzstan must be the origin of the plague strain that caused the Black Death, as two ancient plague genomes that the team collected from teeth revealed one the only strain of plague that is the latest direct precursor to this big bang. This puts him right at the very beginning of the outbreak of the Black Death and before he arrived in Europe.
“We found that ancient strains from Kyrgyzstan are positioned at the heart of this massive diversification event,” said study lead author Maria Spiro, a postdoctoral fellow at the University of Tübingen in Germany.
Additional evidence to support the researchers’ claim comes from comparing plague strains found in modern rodents with those sequenced from cemeteries. They found that modern plague strains, which are most closely related to the ancient strain, are now found in wild rodents, such as marmots living in the Tien Shan Mountains, very close to the two cemeteries.
“What is really remarkable is that today, in rodents living in this region, we have the closest living relatives of this strain of the Big Bang (plague bacteria),” said senior study author Johannes Krause, director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
“We found not only the ancestor of the Black Death, but we actually discovered the ancestor of most of the plague strains circulating in the world today.”
There are still many things that the team does not know, such as which animal the disease spread to humans. But understanding the origins of the biggest pandemic in human history could help prepare for future disease outbreaks, Krause said.
“Just like Covid, the Black Death was a new disease and the beginning of a huge pandemic that lasted about 500 years. It is very important to understand the circumstances under which it appeared, “Krause said.
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