A Refined Phylochronology of the Second Plague Pandemic in Western Eurasia

Although dozens of ancient Yersinia pestis genomes and a vast corpus of documentary data are available, the origin and spread of consecutive outbreaks of the Second Plague Pandemic in Europe (14th-18th c.) are still poorly understood. For the majority of ancient genomes, only radiocarbon dates spanning several decades are available, hampering an association with historically recorded plague outbreaks. Here, we present new genomic evidence of the Second Pandemic from 11 sites in England, Estonia, the Netherlands, Russia, and Switzerland yielding 11 Y. pestis genomes with >4-fold mean coverage dating to between 1349 and 1710. In addition, we present a novel approach for integrating the chronological information retrieved from phylogenetic analysis with their respective radiocarbon dates, based on a novel methodology offering more precise dating intervals. Together with a fine-grained analysis of documentarily recorded plague outbreaks, this allows us to tentatively associate all available Y. pestis genomes of the Second Pandemic with historically documented plague outbreaks. Through these combined multidisciplinary analytical efforts, our newly sequenced genomes can be attributed to the Black Death in Cambridge (England), the pestis tertia or pestis quarta in the late 14th century (Estonia), previously unknown branches emerging in the 15th century (Estonia, the Netherlands and England), and a widespread pandemic in Eastern Europe around 1500 (western Russia), which all seem to have originated from one or multiple reservoirs located in Central Europe. While the latter continued to harbour a major Y. pestis lineage at least until the 1630s, represented by new genomes of the Thirty Years War plague (Switzerland), another lineage consecutively spread into Europe between the 17th and 18th century from the Ottoman Empire, as evidenced by a genome associated with the Great Northern War plague (Estonia). By combining phylogenetic analysis with a systematic historical reconstruction based on textual sources and an innovative phylogenetically informed radiocarbon modelling (PhIRM), we offer a new groundbreaking interdisciplinary approach that solves several fundamental methodological challenges associated with phylogenetic and spatio-temporal reconstruction of historical pandemics.