For generations, the scientific understanding of plague has been anchored to a specific image: densely crowded medieval cities, ship-borne rats, and the flea-rodent-human transmission chain that unleashed the Black Death across Europe in the 14th century. That picture, which positioned urban density as a prerequisite for plague outbreaks, has now been fundamentally challenged.
A study published in Nature on June 18, 2026 by an international collaboration of geneticists, archaeologists, and bioinformaticians — led by Professor Eske Willerslev of the Globe Institute, University of Copenhagen, and the University of Cambridge — has confirmed that Yersinia pestis, the bacterium responsible for bubonic, pneumonic, and septicemic plague, was already causing deadly outbreaks in small hunter-gatherer populations near Lake Baikal in southeast Siberia approximately 5,500 years ago. This predates the first cities, domestic rat populations, and the emergence of the flea-borne transmission pathway by thousands of years.
