Plague infections were common in humans 3,300 years earlier than the historical record suggests, reports a study published October 22 in Cell. By sequencing the DNA of tooth samples from Bronze Age individuals from Europe and Asia, the researchers discovered evidence of plague infections roughly 4,800 years ago. But it was at least another thousand years until the bacterium that causes the disease, Yersinia pestis, acquired key changes in virulence genes, allowing it to spread via fleas and evade the host immune system.
"We found that the Y. pestis lineage originated and was widespread much earlier than previously thought, and we narrowed the time window as to when it developed," says senior study author Eske Willerslev of the Center for GeoGenetics, University of Copenhagen. "This study changes our view of when and how plague influenced human populations and opens new avenues for studying the evolution of diseases."
Y. pestis was the notorious culprit behind the sixth century's Plague of Justinian, the Black Death, which killed 30%-50% of the European population in the mid-1300s, and the Third Pandemic, which emerged in China in the 1850s. Earlier putative plagues, such as the Plague of Athens nearly 2,500 years ago and the second century's Antonine Plague, have been linked to the decline of Classical Greece and the undermining of the Roman army. However, it has been unclear whether Y. pestis could have been responsible for these early epidemics because direct molecular evidence for this bacterium has not been obtained from skeletal material older than 1,500 years.
Ancient DNA analyses of skeletal remains of plague victims from the 6th century AD provide information about the phylogeny and the place of origin of this pandemic
From the several pandemics generally called 'pestilences' three are historically recognized as due to plague, but only for the third pandemic of the 19th to 21st centuries AD there were microbiological evidences that the causing agent was the bacterium Yersinia pestis. "For a long time scholars from different disciplines have intensively discussed about the actual etiological agents of the past pandemics. Only ancient DNA analyses carried out on skeletal remains of plague victims could finally conclude the debate", said Dr. Barbara Bramanti of the Palaeogenetics Group at the Institute of Anthropology at Johannes Gutenberg University Mainz (JGU). About two years ago, she headed the international team which demonstrated beyond any doubt that Y. pestis also caused the second pandemic of the 14th-17th centuries including the Black Death, the infamous epidemic that ravaged Europe from 1346 to 1351. Bramanti and her Mainz colleague Stephanie Hänsch now cooperated with the University of Munich, the German Bundeswehr, and international scholars to solve the debate as to whether Y. pestis caused the so-called Justinianic Plague of the 6th to 8th centuries AD. The results of ancient DNA analyses carried out on the early medieval cemetery of Aschheim in Bavaria were published last week in PloS Pathogens. They confirmed unambiguously that Y. pestis was indeed the causing agent of the first pandemic, in contrast to what has been postulated by other scientists recently. This revolutionary result is supported by the analysis of the genotype of the ancient strain which provide information about the phylogeny and the place of origin of this plague. As for the second and third pandemic, the original sources of the plague bacillus were in Asia.
