London: Scientists studying ancient DNA have uncovered new clues about how the plague kept returning to haunt Europe for around 400 years after the Black Death, one of the deadliest pandemics in human history.

The Black Death swept through Europe, Asia, and North Africa in the mid-1300s, killing an estimated tens of millions of people. But the horror did not end there. Wave after wave of plague outbreaks struck European cities for centuries afterwards, from the 1400s right through to the 1700s.

For historians, the puzzle was always the same: where did the disease hide between outbreaks, and why did it keep coming back? The new genetic evidence offers the clearest answers yet.

What the ancient DNA shows

By extracting and sequencing DNA of the plague bacterium, Yersinia pestis, from the remains of medieval victims, researchers can track how the pathogen evolved over time. The genetic trail suggests the bacteria established long-term reservoirs in wild rodent populations, from which it repeatedly spilled over into human communities.

Trade routes, troop movements, and growing cities then carried infected rats and fleas from place to place, reigniting outbreaks in populations with little immunity. Small genetic changes in the bacterium may also have helped it adapt and persist across the centuries.

Why it matters today

Plague still exists in parts of the world, including Madagascar, the Democratic Republic of Congo, and the western United States, though modern antibiotics make it treatable when caught early. Understanding how it entrenched itself for centuries helps epidemiologists think about how today’s pathogens might behave.

The study is also a showcase for ancient DNA as a historical detective tool. Bones and teeth that sat in the ground for 600 years are now yielding genetic testimony, letting science reconstruct pandemics that written records could only describe in fear and confusion.