Bengaluru: German scientists say they have finally discovered the origins of the deadliest pandemic in recorded history, the medieval bubonic plague, using DNA sequencing.
Also known as the ‘Black Death’, the plague that spread through Eurasia and Northern Africa between 1346 and 1353 was one of the largest infectious disease episodes in human history, drastically reducing the world’s population. While studies have put the toll at 25 million, estimates suggest the number of fatalities could have reached 200 million.
While the plague’s spread and symptoms have been meticulously documented and its global impact widely understood, its origins — the first particular bacterium strain and where it all began — remained a mystery until now.
A German research team has conducted DNA analysis of seven individuals who died in the 14th century and sequenced the strain of the original bacterium Yersinia pestis (Y. pestis), which was responsible for the disease. The findings, which have been peer-reviewed, were published Wednesday in the British scientific journal Nature.
The study also concluded that the plague originated in central Eurasia, likely in the Tian Shan region of modern-day Kyrgyzstan.
Previous genetic analyses of DNA extracted from graves had indicated that a strain of the bacterium Y. pestis was definitively to blame for the plague. However, over the years, four major lineages of this bacteria were identified, whose descendants can still be found in rats today, according to the latest study.
While the existing strains have been identified, a historic record of the plague bacterium’s evolutionary tree has been missing because of a largely Eurocentric focus in research, explain the authors. Scientists, however, know that it underwent a diversification event, leading to the present lineages.
Looking for answers, in graves
To trace its origins, the research team went back to the location of the earliest mention of the plague — Central Asia. Records of people dying in the Tian Shan region prompted the researchers to examine a medieval grave in Lake Issyk-Kul of Kyrgyzstan.
Archaeological records indicate that a disproportionately high number of burials occurred in neighbouring graves between 1338 and 1339, and many gravestones simply noted the cause of death as ‘pestilence’.
The authors compared archaeological, historical and genetic data of seven individuals buried here. They found the Y. pestis bacterium in three of the samples and noted that they were all the same strain.
Further analysis revealed that the strain was a common ancestor of the bubonic plague strains that have since been identified and are also present today in rats.
“We found that the ancient strains from Kyrgyzstan are positioned exactly at the node of this massive diversification event. In other words, we found the Black Death’s source strain and we even know its exact date [the year 1338],” said Maria Spyrou, lead author of the study and researcher at the University of Tübingen, in a press release.
Archaeological data further revealed that this region had lots of diverse communities of people that intermingled and was a prime trade hub across Eurasia in the 14th century. The authors propose that active trade contributed to the rapid spread of the plague.
The deathly spread & resultant upheaval
The Bubonic plague has been recorded as first having infected Central Asia, before moving on to Southeast and South Asia, before spreading via Northern Africa in Northern Europe, and ultimately reaching Siberia. The disease spread through land and sea trade routes.
As it cut down the global population by millions, its impact was felt in the form of economical and societal upheaval all over the world.
The massive fatality rate resulted in a large demand for labour from among the surviving population. This ultimately resulted, a few decades later, in prosperity, setting the stage for the ‘Age of Exploration’, starting in the 1400s and continuing through the 1600s in Europe.
However, there were many immediate detrimental impacts.
Since the origins and spread of the plague could not be explained, there was tremendous civil unrest and clashes between communities. Many large cities across all Eurasia and Northern Africa fell into despair as other infestations and diseases spread. There was also a decline in the rate of growth of population, and an increase in famine and malnutrition globally.
In Europe, this consequently led to laws protecting farmers and workers, and an increase in innovation, which was followed by an influx of wealth over the next decades and centuries as colonisation began.
However, the plague’s effects on Asian and African nations are less documented and studied because of the historic Eurocentric focus in research.
(Edited by Zinnia Ray Chaudhuri)