Black Death’s true origins revealed – and it’s not rats
Buck-toothed and fluffy, the marmot might seem a relatively harmless rodent, but new research suggests it could have been to blame for killing half of Europe.
The origin of the Black Death has finally been pinpointed to the Tian Shan region of north Kyrgyzstan, where a marmot spillover event is likely to have seeded plague into a community of Christian traders, who then spread the disease via the Silk Road.
Inscriptions on gravestones near Lake Issyk Kul had already shown that an epidemic of “pestilence” devastated the area in 1338 and 1339, nine years before the plague entered the Mediterranean via trade ships.
But now DNA sequencing on teeth from the graves have proven the dead were riddled with an early ancestral form of Yersinia pestis, the bacterium responsible for bubonic plague.
A similar strain of the same bacteria has also been found in living marmot populations around the lake, providing confirmatory evidence that the site is ground zero.
Dr Philip Slavin, a historian from the University of Stirling, Scotland, said: “Our study puts to rest one of the biggest and most fascinating questions in history and determines when and where the single most notorious and infamous killer of humans began.
“We studied specimens from two cemeteries near Lake Issyk Kul in what is now north Kyrgyzstan after identifying a huge spike in the number of burials there in 1338 and 1339.
“When you have one or two years with excess mortality it means something funny was going on there, and it wasn’t just any year, it was just seven or eight years before the Black Death came to Europe.
“We then discovered that this site had in fact 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 studying the historic diaries of the original grave excavations in order to match the individual skeletons to their headstones, carefully translating the inscriptions, which were written in Syriac language.
Despite the high risk of environmental contamination and no guarantee that the bacteria would have been preserved, the team was able to get 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 trace these skeletons and analyse DNA taken from the teeth,” added Dr Salvin.
“To my astonishment, this confirmed the beginning of the second plague pandemic.”
The Black Death was first detected in the 1330s and within just a few decades had disseminated across Europe, the Middle East and northern Africa claiming up to 60 per cent of the population, and lasting 500 years.
One of largest infectious disease catastrophes in history
It is considered one of the largest infectious disease catastrophes in human history, but despite intense multidisciplinary research, its geographic and chronological origins have never been identified, with many speculating its origin was China.
Plague is not a disease of humans; the bacterium survives within wild rodent populations across the world, in so-called plague reservoirs and it spreads to humans through fleas on the animals.
The team believes that the plague jumped into humans via marmots, which sparked a “Big Bang” event allowing the disease to diversify and evolve into new kinds of bacteria, many of which survive today.
“We found that modern strains most closely related to the ancient strain are today found in plague reservoirs around the Tian Shan mountains, so very close to where the ancient strain was found,” said Prof Johannes Krause, senior author of the study and director at the Max Planck Institute for Evolutionary Anthropology.
“The marmots still carry it and there have been thousands of plague strains analysed all over the world, but the closest are found in that particular location.
“We even take this a step further and suggest that marmots or other rodent populations had something to do with the spillover event that led to the epidemic we describe in 1338.”
The plague largely disappeared in the 18th century with improvement of hygiene and the demise of the black “plague” rat which was replaced by the brown rat.
Yet there are still some reservoirs, particularly in remote areas of the western US and hunters are often infected by flares in outbreaks from prairie dogs.
Although the disease is currently easily treatable with antibiotics, if antibiotic resistance were to arise in the future, it is possible that the Black Death could return.
“If there was antibiotic resistance to the strain then it would come back at the 60 per cent death rates of the past which would be quite horrible for the thousands of people who get infected every year,” added Prof Krause.
The research was published in the journal Nature.