New Study Maps Black Death Plague Returns Across Europe Until the 18th Century

Textbooks and history classes often present the Black Death as a single catastrophic bout of plague that swept through Europe from 1347 to 1353. Yet the disease’s history continued for several more centuries.

A new study in PNAS, led by researchers at the University of Tartu in Estonia, shows that plague repeatedly returned to different parts of Europe until the 18th century.

Although the second plague pandemic has long been known about, it has not previously been mapped with this degree of detail or dated so precisely.

Mapping the second plague pandemic

The team developed a new way to match plague genomes with recorded historical outbreaks. By using additional evidence from the evolutionary tree of the bacterium Yersinia pestis, they were able to determine more accurately when and where distinct strains emerged.

"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," says molecular biologist Kristiina Tambets, from the University of Tartu.

Researchers reconstructed and analysed 26 Y. pestis genomes obtained from 11 archaeological excavations in Estonia, Russia, England, the Netherlands and Switzerland.

Their method brought together conventional radiocarbon dating, genetic chronological timelines, historical archives and local mortality records. In total, it enabled more accurate dating for 75 plague genomes: 11 higher-quality samples among the newly recovered 26 DNA fragments, along with 64 samples examined in previous studies.

"We were able to improve dating intervals for many samples, which allowed us to connect them to specific plague waves and outbreaks that were recorded in the respective towns or regions by chroniclers," says historian Philip Slavin, from the University of Stirling in the UK.

Yersinia pestis lineages, drought and conflict

One of the key findings from this more granular analysis was substantial diversification in Y. pestis lineages - branches of its evolutionary tree - between around 1450 and 1500. This may have created new rodent reservoirs for plague.

The researchers also identify a possible link with the Great Renaissance Drought, which occurred during roughly the same period. The drought may have caused wild rodents to die in greater numbers or move closer to human settlements, helping to spread disease.

The analysis also connected plague outbreaks with the Thirty Years' War of 1618–1648 and the Great Northern War of 1700–1721. It suggests that armies, refugees, traders and other populations travelling in large groups commonly carried infections with them.

"We see how Yersinia pestis splits into new branches during periods of conflict and spreads along the routes traveled by troops and displaced populations," says geneticist Christiana Scheib, from the University of Tartu.

As further ancient DNA is recovered and assembled, this timeline could become still more accurate, allowing links with historical events to be made with greater confidence.

Lessons from historical plague for modern pandemics

Yersinia pestis remains present today. Human plague cases are now very rare and can be treated successfully with modern antibiotics, but the study still offers lessons for present-day disease threats.

The findings provide further context for understanding how diseases that pass from animals to humans develop over time - in this case, across several centuries. Should the threat of another pandemic arise, researchers may be better placed to assess and model it.

This investigation of a historic disease could therefore help shape responses to the next threat, supported by modern medicine and analytical techniques.

"With COVID-19, scientists could reconstruct the spread of individual strains extremely well because the genomes came with precise timestamps," says geneticist Marcel Keller, from the University of Tartu.

"For historical pandemics, those timestamps are often missing or may cover more than 100 years, which limits our ability to interpret the genetic data."

The research has been published in PNAS.

This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.