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.