A phylogeography of the second plague pandemic revealed through the analysis of historical Y. pestis genomes

The second plague pandemic (14th - 18th century AD), caused by the bacterium Yersinia pestis , is infamous for its initial wave, the Black Death (1346-1353 AD), and its repeated scourges in Europe and the vicinity until the Early Modern Era. Here, we report 32 ancient Y. pestis genomes spanning the 14th to 17th century AD through the analysis of human remains from nine European archaeological sites. Our data support an initial entry of the bacterium from Eastern Europe and the absence of genetic diversity during the Black Death as well as low diversity during local outbreaks thereafter. Moreover, analysis of post-Black Death genomes shows the diversification of a Y. pestis lineage into multiple genetically distinct clades that may have given rise to more than one disease reservoir in, or close to, Europe. Finally, we show the loss of a genomic region that includes virulence-associated genes in strains associated with late stages of the second plague pandemic (17th - 18th century AD). This deletion could not be detected in extant strains within our modern dataset, though it was identified in a today-extinct lineage associated with the first plague pandemic (6th - 8th century AD), suggesting convergent evolution during both pandemic events.