Ancient DNA Shows Plague Rose Again and Again for Four Centuries After the Black Death

The Black Death of the mid‑1300s is famous for wiping out a huge slice of Europe’s population in a few short years. Yet, contrary to the popular belief that the pestilence vanished after that cataclysm, new research shows it kept turning up like an unwelcome guest at a centuries‑long party.

In a study led by scientists at the University of Tartu, investigators dug into the bones of people who died between the 1300s and the 1700s. From these ancient remains they extracted DNA of Yersinia pestis – the bacterium responsible for plague – and managed to piece together 26 fairly complete genomes. The samples came from 11 sites scattered across Estonia, Russia, England, the Netherlands and Switzerland, offering a broad snapshot of the so‑called Second Plague Pandemic.

What emerged was far from a simple story of a single source spreading outward. Instead, the genetic data suggest that plague re‑entered Europe on several occasions, establishing new reservoirs in both towns and the wild. Estonia, for instance, appears to have been hit multiple times, its trade links acting like highways for the disease.

One especially intriguing episode unfolded between 1450 and 1500. During those decades the bacterial lineages underwent a rapid expansion, branching into three major groups. Those branches likely seeded fresh pools of infection among wild rodents – the natural hosts that keep Y. pestis alive when humans are not around. The researchers even point to the Great Renaissance Drought as a possible climate driver, noting how dry spells can tip the ecological balance in favour of rodent‑borne outbreaks.

“We found evidence for repeated introductions of plague into Estonia starting already in the late 14th century and identified several previously unknown genetic lineages, both in urban and rural settings,” explains senior author Prof. Kristiina Tambets.

Beyond mapping the spread, the team tackled a thorny methodological problem: dating ancient pathogen DNA. Unlike modern pandemics such as COVID‑19, where every viral genome is attached to a precise calendar date, ancient samples usually come with only broad radiocarbon ranges that can span decades. To sharpen the timeline, the researchers placed each plague genome onto the bacterium’s evolutionary tree and used its position to narrow down when it likely existed.

This trick let them re‑date 64 previously published genomes and the 11 new ones with far more confidence. The result? A near‑complete alignment of genetic evidence with historic chronicles, linking many ancient strains to specific plague waves recorded by contemporary observers.

Human drama also left its mark on the pathogen’s genealogy. The study highlights how massive conflicts – the Thirty Years’ War (1618‑1648) and the Great Northern War (c. 1700‑1721) – acted as vectors for disease. Troops, refugees and merchants moving along the same routes gave Y. pestis fresh opportunities to hop between populations, spawning new branches in the bacterial family tree.

“We see how Yersinia pestis splits into new branches during periods of conflict and spreads along the routes travelled by troops and displaced populations,” says senior author Dr. Christiana L. Scheib, noting the 1710 siege of Tallinn as a stark example where both Swedish and Russian soldiers fell victim.

All told, plague was not a one‑off medieval nightmare but a recurring specter that haunted Europe for more than four hundred years. Understanding this long‑term pattern matters today because Y. pestis still survives in rodent reservoirs worldwide. By learning how the bacterium once slipped back into human societies, we can better anticipate where it might re‑emerge.

As the authors conclude, the combination of ancient DNA, refined dating and historical records offers a powerful template for investigating other forgotten pandemics – a reminder that the past still speaks loudly to the present.