The Circulation of Yersinia pestis in Central Eurasia before and during the First Plague Pandemic (Second to Eighth Century CE): Palaeogenetic and Historical Evidence and Sociopolitical, Ecological, and Climatic Factors

Modern Yersinia pestis genomes show the greatest diversity of the plague pathogen in Central Eurasia. This region is now widely linked to the origins of the Y. pestis lineages responsible for two historic plague pandemics: one starting with the so-called “Justinianic Plague” of the mid-sixth century and the other with the “Black Death” of the mid-fourteenth century. These pandemics have mostly been studied in the Mediterranean region and Europe. Although the beginning of the latter is clearly defined both geographically and temporally, the early spread of the former has received less attention, despite being the focus of several competing hypotheses. Here, we build on recent discoveries of Y. pestis in late antique human remains from Central Eurasia and Europe. These findings identified an early victim of the Y. pestis lineage in Central Eurasia, centuries before it appeared in Europe during the Justinianic Plague. We contextualize these analyses with (I) what we can reconstruct from archaeological, written, and paleoclimate evidence about the demographic, economic, environmental, and mobility (human and animal) histories of the region in the earliest centuries CE, and (II) written evidence for epidemic disease from the region and neighboring areas, which may be linked to the spread of the plague before, during, and after the Justinianic Plague. Specifically, we examine sources to establish and evaluate hypotheses about how, why, and if the plague spread from Central Eurasia, ultimately causing the Justinianic Plague and the “First Plague Pandemic,” and how significantly Eurasian populations were impacted over these centuries. Despite extensive source analysis, limited information, especially palaeogenomic data, prevents us from definitively pinpointing the immediate origin of the First Plague Pandemic. Still, most evidence strongly suggests that the Y. pestis lineage originated from Central Eurasia.