Ancient Plague’s Origins Revealed Through Sheep DNA Discovery

Researchers have uncovered significant evidence of the ancient plague bacterium, Yersinia pestis, in the tooth of a Bronze Age sheep. This finding provides a fresh perspective on how the disease spread throughout Eurasia during the Bronze Age, challenging long-held assumptions about its transmission mechanisms.

The analysis reveals that this earlier variant of the plague, which existed well before the devastating Black Death that swept through Europe in the Middle Ages, was not primarily spread by fleas as previously thought. Instead, the study suggests that close interactions between humans and domesticated animals, particularly sheep, may have facilitated the disease’s widespread transmission.

The research team, which includes archaeologist Taylor Hermes from the University of Arkansas, discovered DNA from Yersinia pestis in a sheep tooth unearthed in what is now southern Russia. This groundbreaking finding, published in the journal Cell, marks the first known instance of the ancient plague affecting animals, not just humans.

Understanding the Transmission of the Plague

Hermes emphasized the importance of this discovery, stating, “It was alarm bells for my team. This was the first time we had recovered the genome from Yersinia pestis in a non-human sample.” The researchers faced significant challenges in isolating ancient DNA from the tooth due to contamination from soil, microbes, and modern human DNA. The DNA fragments they managed to recover were often severely damaged and extremely small, making the process of analysis particularly complex.

This new evidence suggests that the plague could have spread through close contact not only between humans but also involving livestock and wildlife, coinciding with the Bronze Age’s advancements in animal herding and travel. Societies during this period began keeping larger herds and moving across greater distances, conditions that may have accelerated the transfer of pathogens.

The study posits that sheep likely contracted the bacterium from other animals, such as rodents or migratory birds, which carried the pathogen without showing signs of illness. The findings highlight the ongoing risk of zoonotic diseases—those that jump from animals to humans—especially as human populations encroach on new environments and interact more closely with wildlife.

Future Directions in Research

While this study is a significant step forward, researchers caution that conclusions drawn from a single ancient sheep genome are limited. They plan to investigate additional ancient human and animal remains from the region to better understand the scope of the plague’s reach and the various species involved in its spread.

Additionally, the researchers aim to identify the original wild animal that carried the bacteria and to clarify how human movement and livestock herding contributed to the disease’s dissemination across vast territories. These insights could prove invaluable in predicting how animal-borne diseases continue to emerge in modern times.

Led by scientists from the Max Planck Institute for Infection Biology, with senior authors Felix M. Key and Christina Warinner from both the Max Planck Institute and Harvard University, this research highlights the need for greater respect for the interconnectedness of human health and environmental forces.

The Max Planck Society supported this study and is funding further investigations in the region. As researchers continue to unravel the complexities of ancient diseases, they hope their findings will inform current public health strategies and enhance our understanding of zoonotic disease transmission.