Ancient DNA Sheds Light on Spread of Plague in Medieval Denmark

By analyzing DNA obtained from fragments of ancient teeth, a team of led by scientists from McMaster University has gained new insights into the evolution of the plague over hundreds of years in medieval Denmark. The plague, caused by the bacterium Yersinia pestis, is responsible for several devastating pandemics across Europe, Asia, and Africa during the Middle Ages. Its historical epidemiology, however, is controversial due to the scarcity and ambiguity of available data. To better understand the disease's spread in Scandinavia, the researchers performed in-depth longitudinal screening for Y. pestis across archaeological sites in Denmark, identifying the bacterium's DNA in tooth samples from 13 individuals who lived at different times between the 14th and 17th centuries. As reported in Current Biology this week, they used the DNA to reconstruct and analyze Y. pestis genomes, revealing the continual evolution and reintroduction of bacterial strains throughout waves of plague infections. The analysis, the study's authors write, shows that the Danish Y. pestis sequences were "interspersed with those from other European countries rather than forming a single cluster, indicative of the generation, spread, and replacement of bacterial variants through communities rather than their long-term local persistence. These results provide an epidemiological link between Y. pestis and the unknown pestilence that afflicted medieval and early modern Europe," as well as highlight the utility of population-scale genomic evidence for historical disease research, they add.