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An international team of researchers has badyzed the human remains of 21 archaeological sites to learn more about the impact and evolution of the bacteria responsible for the plague. Yersinia pestis during the first plague pandemic (541-750 AD). In a study published in PNAS, the researchers reconstructed 8 plague genomes from Britain, Germany, France and Spain and uncovered a level of previously unknown diversity Y. pestis strains. In addition, they found the first direct genetic evidence of Justinian plague in the British Isles.
The Justinian plague began in 541 in the eastern Roman Empire, then ruled by Emperor Justinian I, and recurring epidemics ravaged Europe and the Mediterranean basin for about 200 years. Contemporary archives describe the extent of the pandemic, which would have destroyed up to 25% of the population of the Roman world at the time. Recent genetic studies have revealed that the bacterium Yersinia pestis was at the origin of the disease, but it was unclear until then how it had spread and how the strains emerged during the pandemic were related.
In this study, an international team of researchers led by the Max Planck Institute for the Science of Human History badyzed human remains from 21 sites with multiple burials in Austria, Great Britain, Germany , in France and Spain. They were able to rebuild 8 new Y. pestis genomes, allowing them to compare these strains with ancient and modern genomes previously published. In addition, the team discovered the oldest genetic evidence of plague in Britain, from the Anglo Saxon site of Edix Hill. By combining archaeological dating and the position of this strain of Y. pestis in its evolutionary tree, the researchers concluded that the genome was probably linked to a plague described ambiguously in the British Isles in 544 AD.
High diversity of Y. pestis strains during the first pandemic
The researchers discovered that there was previously unknown diversity of Y. pestis circulating in Europe between the 6th and the 8th century AD. The 8 new genomes came from Britain, France, Germany and Spain. "The recovery of genomes covering a vast geographic and temporal scope gives us the opportunity to evaluate Y. pestis"Microdiversity is present in Europe during the first pandemic," says co-lead author Marcel Keller, a PhD student at the Max Planck Institute for the Science of Human History, currently working at the University of California. University of Tartu. Recently discovered genomes have revealed the closely related strains of Y. pestis circulating during the 200 years of the first pandemic, some possibly at the same times and in the same regions.
Despite the greatly increased number of genomes now available, researchers have not been able to clarify the occurrence of Justinian plague. "The lineage probably appeared in Central Asia several hundred years before the first pandemic, but we estimate that current data are insufficient to resolve the origin of Justinian plague as a human epidemic, before it's first reported in Egypt in 541 AD the fact that all genomes belong to the same lineage is indicative of a persistence of plague in Europe or the Mediterranean Basin during of this period, instead of multiple reintroductions. "
Possible proof of convergent evolution of strains from two independent historical pandemics
Another interesting conclusion from the study is that the plague genomes appearing towards the end of the first pandemic show a significant deletion in their genetic code that includes two virulence factors. The plague genomes of the later stages of the second pandemic, 800 to 1000 years later, show a similar deletion covering the same region of the genomes. "This is a possible example of convergent evolution, which means that these Y. pestis strains independently developed similar characteristics. Such changes may reflect an adaptation to a distinct ecological niche in western Eurasia, where the plague was transmitted during both pandemics, "says Maria Spyrou, co-premier author of the Max Planck Institute for the Science of Cancer. Human history.
This study provides new information on the first historically documented plague pandemic and provides additional clues along with historical, archaeological and paleoepidemiological evidence, helping to answer outstanding questions. "This study demonstrates the potential of paleogenomic research for understanding historical and modern pandemics by comparing genomes over millennia," says lead author Johannes Krause of the Max Planck Institute for the Science of Cancer. 39, human history. "With a larger sample of possible burials, we hope to contribute to the understanding of Y. pestis"Microevolution and its impact on humans during past and present pandemics".
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