Scientists studying the origins and evolution of the plague have examined hundreds of ancient human teeth from Denmark, seeking to answer long-standing questions regarding its arrival, persistence and spread in Scandinavia.
In the first longitudinal study of its kind, looking at a single region for 800 years (between 1000 and 1800 AD), researchers reconstructed Yersinia pestis genomes, the bacterium that caused the plague, and showed that it was reintroduced to the Danish population from other parts of Europe once more and once more, possibly through human movement, with devastating effects.
The historical samples were taken from nearly 300 individuals located at 13 different archaeological sites across the country.
“We know that plague epidemics across Europe continued in waves for around 500 years, but very little regarding its spread through Denmark is documented in historical records,” says Ravneet Sidhu, one of the study’s lead authors and a graduate student at McMaster’s Ancient DNA Center. , where the analysis was performed.
McMaster researchers, in collaboration with a team of historians and bioarchaeologists from Denmark and Manitoba, carried out an in-depth examination of the connections and differences between the different strains of plague present in Denmark at that time.
They reconstructed and sequenced the genomes of Y. pestis, using fragments extracted from old teeth, which can retain traces of blood-borne infection for centuries. They compared the plague genomes to each other and to their present-day relatives.
The researchers found positive plague samples from 13 individuals who had lived and died over a period of three centuries.
Nine of these samples provided enough genetic information to draw evolutionary conclusions regarding the persistence of plague in Denmark. The results create a picture of urban and rural populations hammered by relentless waves of plague.
“The high frequency of Y. pestis reintroduction to Danish communities is consistent with the assumption that most deaths during the period were due to newly introduced pathogens. This association between the introduction of pathogens and mortality sheds light on key aspects of demographic change, not only in Denmark but across the European continent,” says Jesper L. Boldsen, Curator of the Skeleton Collection and paleodemographer at ADBOU, University of Southern Denmark.
The analysis, published today in the journal Current biologyrevealed that the Danish Y. pestis the sequences were interspersed with medieval and modern strains from other European countries, including the Baltic region and Russia, rather than coming from a single domestic group that re-emerged from natural reservoirs over the centuries.
“Evidence of the plague in Denmark, both historical and archaeological, has been much scarcer than in some other regions, such as England and Italy. This study identified the plague for the first time in medieval Denmark, allowing us to relate the experience in Denmark to disease patterns elsewhere,” said Julia Gamble, study co-author and assistant professor of anthropology at the University of Manitoba.
In startling detail, researchers describe the first known appearance of Y. pestis in Denmark in the town of Ribe dating from 1333 during the Black Death, its appearance in rural areas such as Tirup — where there is no surviving historical evidence — and its disappearance around 1649.
Most of the places affected in Denmark were port towns, but one of the latest outbreaks hit a small rural site in the center of the country with no access to water, suggesting an overland importation.
Plague is a disease of rodents, but the results clearly suggest human-facilitated movement of plague, either via rodents traveling with humans or other vectors, such as lice, on them.
“The findings reveal new links between past and present plague experiences and add to our understanding of the distribution, patterns and virulence of re-emerging diseases,” says Hendrik Poinar, lead author of the paper, director of the McMaster Ancient DNA Center. and researcher at the Michael G. DeGroote Institute for Infectious Disease Research.
“We can use this study and the methods we have employed for the study of future pandemics,” he says.
