Denture and cuddly, the marmot may seem like a relatively harmless rodent, but new research suggests it may have been to blame for killing half of Europe.
The origin of the Black Death was eventually identified in the Tian Shan region of northern Kyrgyzstan, where a marmot spread event likely seeded the plague in a community of Christian traders, who then spread the disease along the Silk Road.
Inscriptions on tombstones near Lake Issyk Kul had previously shown that an epidemic of “pestilence” ravaged the area in 1338 and 1339, nine years before the plague entered the Mediterranean via commercial ships.
But now DNA sequencing on teeth from the graves has proven that the dead were filled with an ancestral form of Yersinia pestis, the bacterium responsible for the bubonic plague.
A similar strain of the same bacteria was also found in living populations of marmots around the lake, providing confirmatory evidence that the site is ground zero.
Philip Slavin, a historian at the University of Stirling in Scotland, said: “Our study closes one of the biggest and most fascinating questions in history and determines when and where the most notorious and infamous killer of humans began.
“We studied specimens from two cemeteries near Lake Issyk Kul in what is now northern Kyrgyzstan, after identifying a large increase in the number of burials there in 1338 and 1339.
“When you have a year or two with excess mortality, it means something funny was happening there, and it wasn’t just any year, it was just seven or eight years before the Black Death hit Europe.
“We then discovered that this site had been excavated in the late 1880s with around 30 skeletons taken from the graves.”
The research required intricate and painstaking work, with Dr. Slavin and colleagues studied the historical diaries of the original excavations of the graves to match the individual skeletons to their headstones, carefully translating the inscriptions, which were written in the Syriac language.
Despite the high risk of environmental contamination and no guarantee that the bacteria would have been preserved, the team was able to obtain DNA from seven individuals unearthed from two of these cemeteries – Kara-Djigach and Burana in the Chu Valley – and found plague bacteria in three.
“We were able to track these skeletons and analyze the DNA taken from the teeth,” added Dr. Salvin.
“To my surprise, this confirmed the start of the second plague pandemic.”
The Black Death was first detected in the 1330s and within just a few decades it had spread across Europe, the Middle East and North Africa, claiming up to 60% of the population and lasting for 500 years.
One of the biggest infectious disease catastrophes in history
It is considered one of the greatest infectious disease catastrophes in human history, but despite intense multidisciplinary research, its geographical and chronological origins have never been identified, with many speculating that its origin was China.
Plague is not a disease of humans; the bacterium survives within wild rodent populations around the world, in so-called plague reservoirs, and spreads to humans via animal fleas.
The team believes the plague jumped to humans via groundhogs, which triggered a “Big Bang” event, allowing the disease to diversify and evolve into new types of bacteria, many of which survive today.
“We found that the modern strains most closely related to the ancient strain are now found in plague reservoirs around the Tian Shan Mountains, very close to where the ancient strain was found,” said Professor Johannes Krause, senior author of the study and director of the Max Planck Institute for Evolutionary Anthropology.
“Marmots still carry it and thousands of plague strains have been analyzed around the world, but the closest ones are found in this particular location.
“We even took this a step further and suggested that marmots or other rodent populations had something to do with the spillover event that led to the epidemic we describe in 1338.”
The pest largely disappeared in the 18th century with improved hygiene and the disappearance of the “plague” black rat which was replaced by the brown rat.
However, some reservoirs still exist, particularly in remote areas of the western US, and poachers are often infected by prairie dog outbreaks.
Although the disease is currently easily treatable with antibiotics, if antibiotic resistance emerges in the future, it is possible that the Black Death could return.
“If there were antibiotic resistance to the strain, it would go back to the 60% death rates of the past, which would be pretty horrible for the thousands of people who get infected every year,” added Professor Krause.
The research was published in the journal Nature.