Ancient Plague Strain Discovered in Siberia
Recent findings have uncovered ancient DNA from cemeteries in southeast Siberia, revealing a previously unknown strain of plague that had a significant impact on hunter-gatherer communities over 5,500 years ago.
A new study published in the journal Nature suggests these strains may represent the earliest known evidence of plague in human history.
The bacterium Yersinia pestis is responsible for plague, known for sparking some of the deadliest outbreaks in history, notably the Black Death in the 14th century, which claimed around 25 million lives. Before this discovery, the oldest recognized strains associated with bubonic plague had been traced back only about 3,800 years.
Prior to this, it seemed that earlier strains lacked the necessary genetic traits for widespread outbreaks. This raised questions about the bacterium’s origins and how it transmitted from livestock and infected fleas to humans.
Interestingly, the newly identified strain emerged during research aiming to address another issue related to hunter-gatherer remains from Lake Baikal. Notably, researchers found a disproportionate number of children and young adolescents in burial sites, with no visible signs of trauma or death causes.
Analysis of the ancient DNA indicated the presence of plague bacteria in 18 out of 46 individuals from these small, mobile communities, along with a genetic factor that could worsen the severity of infections.
These findings hint at potential origins of the plague and challenge previous concepts about how it spread. “Hunter-gatherers move constantly,” explained Ruairidh Macleod, the lead study author from the University of Oxford. He noted that infectious diseases like these typically don’t devastate isolated communities, as those infected would likely relocate. The evidence suggesting otherwise flips conventional epidemiological theories on their head.
Archaeological excavations in the Lake Baikal area have been ongoing for years, revealing that these communities had rich resources, such as lakes for fishing. This suggests that their burial practices could have been rooted in a long-term connection to the region.
Combining advanced DNA sequencing with archaeological data and radiocarbon dating, the research provided a detailed picture of events from thousands of years ago. Macleod emphasized that the evidence pointed to a swift mass mortality event occurring almost simultaneously among the buried individuals.
Genetic research also illuminated family connections among the deceased, suggesting that the disease spread among relatives who cared for one another, reflecting a historiographical gap in understanding contagion dynamics at that time. Some family members were buried together, possibly indicating they succumbed to the disease during the same outbreak.
On the flip side, some individuals were buried apart, likely due to dying at different times. The study identified two separate outbreaks occurring several hundred years apart within the same region.
One of the astonishing findings revealed that nearly 39% of the graves contained traces of Yersinia pestis infections, potentially revising our perception of early infections of this pathogen.
While the study indicates human-to-human transmission was probable, further research across different sites may be necessary. The researchers extracted ancient bacterial genomes from dental remains, suggesting this unique plague strain originated around 5,700 years ago and differs from all known strains today.
Moreover, the analysis found a unique microbial toxin that seems to have exacerbated infections, disproportionately affecting children aged 7½ to 11. Macleod noted a sorrowful case where several young girls died around the same time, underlining how severely this impacted children’s wellbeing within these communities.
Interestingly, the research highlights the pathway through which these hunter-gatherers likely became infected. Large rodents, particularly marmots, are suspected carriers of the plague bacteria, and it seems the ancient communities hunted and processed these animals, exposing themselves to the bacterium.
Some researchers propose that plague may have originated in Central or Northeast Asia and spread through Eurasia well before complex agricultural societies emerged, long before the crowded populations often associated with subsequent outbreaks.
This research underscores the complexity of ancient plague ecology, revealing how zoonotic diseases were not limited to agricultural societies but also significantly affected hunter-gather cultures. Comments from experts highlight the importance of further exploring how these nomadic lifestyles contributed to disease evolution.
Nonetheless, many questions linger regarding plague’s rapid spread across Northern Eurasia after the Baikal outbreaks. As Macleod pointed out, the gap in timelines poses intriguing possibilities about transmission routes, whether through wildlife or direct human contact.
Tracing the ancient path of plague is essential for understanding pathogen evolution, especially since cases continue to emerge today.
