Cameron Robert Ferguson

One of the most devastating events in human history, the Black Death (c.1347-1353), marked the beginning of the Second Plague Pandemic. After initially receding, plague returned in intermittent outbreaks throughout Europe, beginning with the pestis secunda . Despite its significance, the post-Black Death epidemiology of Yersinia pestis remains poorly understood. Here, we report 23 new Y. pestis genomes recovered from Second Plague Pandemic contexts across Scandinavia, the Netherlands, Iceland, and Armenia, spanning approximately 270 years. Applying a reproducible mutation-filtering pipeline to assess genetic diversity, we report both Black Death and post-Black Death lineages and document multiple waves of plague at individual cemetery sites. We identify four pestis secunda genomes, including three from Armenia, supporting the eastward dissemination of this lineage prior to its disappearance from Europe. We also resolve a previously under-characterised Branch 1A sub-lineage of Y. pestis and provide the first genomic evidence of plague in Iceland, resolving longstanding uncertainty over its presence on the island. Finally, by calling variants against a reconstructed ancestral reference, we identify clade-defining mutations, including nonsynonymous changes in metabolic and biofilm-related genes with predicted structural effects that may have contributed to shaping the epidemiological dynamics of the Second Plague Pandemic.