New genetic research indicates that plague did not disappear from Europe after the Black Death of 1347 to 1353 but returned again and again for more than four centuries. A team led by the University of Tartu, with partners at the University of Cambridge and institutions in the Netherlands and Switzerland, reconstructed the bacterium’s history by reading DNA preserved in the remains of people who died during repeated outbreaks. The findings were published in the Proceedings of the National Academy of Sciences.
The researchers sequenced 26 new genomes of Yersinia pestis, the bacterium that causes plague, and combined them with 64 genomes published in earlier studies. The material came from eleven archaeological sites spread across Estonia, Russia, England, the Netherlands and Switzerland, covering the long stretch known as the Second Plague Pandemic that ran from the fourteenth to the eighteenth century.
The analysis showed that around 1450 to 1500 the surviving plague lineages expanded and split into three separate branches. The authors suggest these branches probably established new reservoirs among rodent populations, giving the disease footholds from which it could resurface in different regions over the following generations rather than dying out after each wave. That pattern helps explain why plague kept striking towns and cities long after the first great outbreak had faded from memory, with fresh epidemics flaring up in one region while another recovered.
To place the ancient genomes in time, the team developed an improved dating method that links genetic samples to specific historical outbreaks. That approach allowed the researchers to match the evolution of the bacterium to documented epidemics and to track how the pathogen moved along trade and migration routes across the continent.
The work adds detail to a long debate over how plague persisted in Europe for so long, and whether repeated waves arrived from outside or grew from reservoirs already present on the continent. Understanding how a pathogen establishes reservoirs, spreads and survives across centuries has value for modern disease surveillance, offering a record of the ways an infection can settle into a landscape and return long after an initial outbreak appears to have passed.
