At the end of the 14th century, Europe suffered one of the greatest cataclysms in its history:the second pandemic of the Black Death. Called the Black Death, this pandemic will decimate more than half of the European population. To better understand the arrival and evolution of the bacterium responsible for the plague, Yersinia pestis , biologists are studying the genome of its different bacterial strains. And recently, a team of researchers was able to analyze ancient bacterial genomes from human remains dating back to the epidemic in order to reconstruct Y's journey. pesti in Europe.
An international team of researchers analyzed the remains of ten archaeological sites located in England, France, Germany, Russia and Switzerland, in order to better understand the different stages of the second plague pandemic (14th-18th centuries) and the genetic diversity of Yersinia pestis during and after the black death.
In a study published in Nature Communications , the researchers reconstructed 34 genomes of Y. pesti s, by retracing the genetic history of the bacterium, which have made it possible to better understand the initiation and progression of the second plague pandemic in Europe.
The second plague pandemic, which began with the Black Death in the mid-14th century and continued with devastating epidemics in and around Europe until the 18th century, decimated the continent, causing the death of nearly 60% of the population. But where does this strain of Yersinia pestis come from? , the bacterium responsible for the plague? And how did it evolve and develop once it arrived in Europe?
Despite the ubiquity of the Black Death in historical texts and popular imagination, the entry point for the bacterium Y. pesti at that time and its route in Europe remain unclear, due to a lack of data on the first outbreaks and a general paucity of data regarding the first genomes of the bacterium.
In the current study, the researchers reconstructed the genomes of plague from the teeth of 34 people, including two from Laishevo, in the Volga region of Russia, and discovered a single ancestral strain from which all the strains of the second pandemic. Additionally, the researchers observed an absence of genomic diversity in samples taken during the Black Death.
“These results indicate a unique entry of Y. pestis into Europe from the East explains the first author, Maria Spyrou. “However, it is possible that additional interpretations may be revealed in future discoveries of unsampled diversity in Western Eurasia .
Although researchers found that the European-wide Black Death was probably caused by a single strain, analysis of genomes from the late part of the pandemic shows the emergence of a lineage with higher genetic diversity.
“During the later phase of the second pandemic, we are witnessing the development of several branches in Europe, which suggests that the plague was maintained in different local foci says Marcel Keller. "No modern descendants of this lineage have been found to date, which may indicate the extinction of these reservoirs .
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The researchers also identified a deletion comprising two virulence-related genes in the genomes of this second lineage. Interestingly, genomes from the later stages of the first plague pandemic showed a deletion in the same region.
“Given that this deletion occurred in the first and second pandemic lineages, both now extinct, determining how the impact of these genes on persistence in humans and fleas would be a important area for future study commented Kirsten Bos, head of the research group at the Max Planck Institute for the Science of Human History.
The study offers new insights into the initiation and progression of the second plague pandemic and adds significantly to Y's genome database. pesti already published. “We have shown that in-depth analysis of ancient Y. pestis genomes can provide unique insights into the micro-evolution of a pathogen over a period of hundreds of years says lead author Johannes Krause.
Going forward, integrating these data into disease modeling efforts, in conjunction with data from other fields such as climatology, epidemiology and history, will be important to better understand the second pandemic. of plague.
