Emergence, continuity, and evolution of Yersinia pestis throughout medieval and early modern Denmark

The historical epidemiology of plague is controversial due to the scarcity and ambiguity of available data.1,2 A common source of debate is the extent and pattern of plague re-emergence and local continuity in Europe during the 14th-18th century CE.3 Despite having a uniquely long history of plague (⠁5,000 years), Scandina-via is relatively underrepresented in the historical archives.4,5 To better understand the historical epidemi-ology and evolutionary history of plague in this region, we performed in-depth (n = 298) longitudinal screening (800 years) for the plague bacterium Yersinia pestis (Y. pestis) across 13 archaeological sites in Denmark from 1000 to 1800 CE. Our genomic and phylogenetic data captured the emergence, continuity, and evolution of Y. pestis in this region over a period of 300 years (14th-17th century CE), for which the plague-positivity rate was 8.3% (3.3%-14.3% by site). Our phylogenetic analysis revealed 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 pesti-lence that afflicted medieval and early modern Europe. They also demonstrate how population-scale genomic evidence can be used to test hypotheses on disease mortality and epidemiology and help pave the way for the next generation of historical disease research.

Automated summary

By investigating 13 archaeological sites in Denmark, a study found that the plague appeared and evolved continuously in the region from the 14th to the 17th century, with cross-interactions with other European countries, rather than long-term local persistence. This research provides epidemiological links between the plague and the unknown pestilence in medieval and early modern Europe, and demonstrates how population-scale genomic evidence can be used to test hypotheses on disease mortality and epidemiology, paving the way for the next generation of historical disease research.