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Researchers trace the evolution and persistence of the plague in medieval Denmark using ancient human teeth

by News Staff
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Researchers have conducted a groundbreaking study on the origins and evolution of the plague in Denmark, utilizing hundreds of ancient human teeth. The aim was to shed light on long-standing questions about the disease’s arrival, persistence, and spread within Scandinavia.

Over a period of 800 years, from 1000 to 1800AD, the scientists reconstructed Yersinia pestis genomes, the bacterium responsible for the plague. They found that the disease was repeatedly reintroduced into the Danish population from other parts of Europe, potentially via human movement, with devastating consequences.

Nearly 300 historical samples were collected from 13 different archaeological sites throughout Denmark, making this the first longitudinal study of its kind, focusing on a single region.

“We know that plague outbreaks continued across Europe in waves for about 500 years, but there is very little documentation on its spread throughout Denmark in historical archives,” explains Ravneet Sidhu, a graduate student at McMaster’s Ancient DNA Center and one of the study’s lead authors.

Collaborating with historians and bioarchaeologists in Denmark and Manitoba, the McMaster researchers conducted a thorough examination of the relatedness and differences between the various strains of plague present in Denmark during this period.

Co-lead author Ravneet Sidhu examines an ancient tooth at McMaster’s Ancient DNA Centre. Credit: Matt Clarke, McMaster University

Using fragments extracted from ancient teeth, researchers reconstructed and sequenced the genomes of Y. pestis, a bacterium responsible for causing the plague, and compared them to modern-day strains. They discovered positive plague samples in 13 individuals who had lived and died in Denmark over a period of three centuries, with nine of those samples providing enough genetic information to draw evolutionary conclusions about the plague’s persistence in the region.

The findings paint a picture of urban and rural communities in Denmark being repeatedly devastated by waves of the plague, indicating a high frequency of Y. pestis reintroduction into these populations. This suggests that many deaths during this period were likely caused by newly introduced pathogens, shedding light on the demographic evolution of not just Denmark, but the entire European continent.

The analysis, published in the journal Current Biology, also revealed that the Y. pestis sequences found in Denmark were not from a single domestic cluster that re-emerged over the centuries, but rather were interspersed with medieval and early modern strains from other European countries such as the Baltic region and Russia.

Remains from the Lindegården excavation site at Ribe Cathedral dated between the 9th and 19th centuries. Credit: Museum of Southwest Jutland

According to Julia Gamble, a co-author and assistant professor of anthropology at the University of Manitoba, evidence for plague in Denmark has been scarce compared to other regions such as England and Italy. However, this study, which identified plague in medieval Denmark for the first time, sheds light on disease patterns across different regions.

The researchers provide detailed accounts of the earliest known appearance of Y. pestis in Denmark, which occurred in the town of Ribe in 1333 during the Black Death. They also found evidence of plague in rural areas like Tirup, where no historical evidence had survived, and observed that most of the outbreaks occurred in port cities. Interestingly, one of the last outbreaks struck a small rural site in the center of Denmark, suggesting that the disease may have been imported via land.

While plague is typically associated with rodents, the results suggest that human-facilitated movement of the disease may have played a role, potentially through rodents traveling with humans or other vectors like lice.

Senior author Hendrik Poinar, director of the McMaster Ancient DNA Center and an investigator with the Michael G. DeGroote Institute for Infectious Disease Research, believes that the study’s methods can be applied to the study of future pandemics. He adds that the findings reveal new connections between past and present experiences of plague, contributing to our understanding of the distribution, patterns, and virulence of re-emerging diseases.

Source: McMaster University

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