Researchers have unearthed a significant breakthrough regarding the ancient plague bacterium, Yersinia pestis, by identifying its DNA in the tooth of a sheep that lived during the Bronze Age. This finding, published in the journal Cell, provides new insights into how the disease spread across Eurasia, challenging longstanding assumptions about its transmission methods.
Long before the notorious Black Death ravaged Europe in the Middle Ages, an earlier version of the plague circulated throughout much of Eurasia, specifically between 3300 and 1200 B.C.. The precise mechanisms behind its widespread transmission during this era had remained a mystery, especially since this ancient strain did not rely on fleas for its spread, as was the case in later outbreaks.
Sheep Offer Surprising Clue
The research team, led by scientists at the Max Planck Institute for Infection Biology, discovered the plague’s genetic material in a sheep tooth found in present-day southern Russia. This evidence marks the first known instance of Yersinia pestis infecting an animal, suggesting that the disease may have had multiple transmission pathways, including from animals to humans.
Study co-author Taylor Hermes, an archaeologist at the University of Arkansas, expressed the significance of the 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 research also highlighted the challenges of isolating ancient DNA from contaminated samples, a task made more difficult by the environmental conditions that affect animal remains.
The researchers faced a complex task of separating tiny fragments of ancient DNA, often damaged and fragmented, from modern contaminants. This meticulous process allowed them to glean insights into how the plague may have spread through interactions between humans, livestock, and wildlife as Bronze Age societies expanded their herding practices and travel.
Implications for Understanding Disease Spread
According to the findings, the close contact between people and their domesticated animals likely facilitated the transmission of the plague. As Bronze Age communities began to maintain larger herds and traveled more extensively, the conditions became ripe for diseases to cross species boundaries.
The study suggests that sheep may have contracted the bacterium from other animals, such as rodents or migratory birds, that carried the disease without suffering from its effects. This phenomenon highlights the ongoing risk posed by zoonotic diseases, which originate in animals and can jump to humans, a concern that persists in today’s world as human encroachment on wildlife habitats increases.
Hermes emphasized the importance of understanding these dynamics, stating, “It had to be more than people moving. Our plague sheep gave us a breakthrough. We now see it as a dynamic between people, livestock, and some still unidentified ‘natural reservoir’ for it.” Researchers are now focused on identifying the original wild animal host of the bacterium and understanding how human behavior and livestock management contributed to its spread across vast distances.
While this study is based on a single ancient sheep genome, researchers acknowledge that further analysis of additional ancient remains is necessary to draw more comprehensive conclusions about the plague’s prevalence and transmission patterns in the Bronze Age. The research team plans to continue their investigations in the region to uncover more about the ancient disease and its interactions with early human societies.
This groundbreaking research, supported by the Max Planck Society, underscores the complex interplay between humans, animals, and diseases, providing a clearer picture of how ancient pathogens may inform our understanding of current and future health challenges.
