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Ancient DNA Points to Plague, Typhoid Pathogens on Greek Island During Bronze Age Transition Period

NEW YORK – The plague-causing pathogen Yersinia pestis as well as Salmonella enterica — the bug behind typhoid/enteric fever — were both present in Crete during an Early Minoan to Middle Minoan Bronze Age transition period marked by massive societal change, new research suggests.

"The occurrence of these two virulent pathogens at the end of the Early Minoan period in Crete emphasizes the necessity to re-introduce infectious diseases as an additional factor possibly contributing to the transformation of early complex societies in the Aegean and beyond," senior and co-corresponding author Philipp Stockhammer, an archaeogenetics researcher affiliated with the Max Plank Institute for Evolutionary Anthropology, the Max Planck Institute for the Science of Human History, and Ludwig Maximillian University, and his colleagues wrote in a paper published Monday in Current Biology.

The researchers used shotgun sequencing to screen dozens of ancient tooth samples from the Hagios Charalambos cave site on Crete's Lasithi plateau for blood-borne pathogens, detecting DNA from known oral bacteria and from the Y. pestis and S. enterica subspecies enterica pathogens.

"[A]rchaeogenetic studies provide an important tool to identify pathogens that affected past populations and, as a result, reveal a more complete picture of their lives and health as well as the pathogens' evolution," the authors wrote.

With the help of enrichment capture sequencing approaches, they put together and characterized pathogen sequences from four infected Bronze Age individuals, ultimately putting together genome sequences for a single Y. pestis isolate and two S. enterica isolates stretching back to roughly 2000 BCE or the end of the 3rd millennium BCE.

By analyzing the genomes alongside other available Y. pestis and S. enterica sequences, the team was able to place the ancient pathogens in broader genetic contexts. The plague-causing Y. pestis isolate fell into an extinct lineage that includes versions of the pathogen that are not adapted for transmission by fleas, for example, while the S. enterica isolates appeared to be part of an extinct lineage that clustered broadly with non-hosted adapted strains of the typhoid/enteric fever-causing bugs still found today.

"The ancient pathogen genomes presented here belong to lineages of Y. pestis and S. enterica that lack any modern representatives," the authors reported, adding that "the virulence and mode of transmission of these two pathogen strains from Hagios Charalambos remains uncertain, as does their potential to cause epidemic events."

More generally, the researchers explained, the findings revealed ties between the pathogens and populations living in the region at the time, pointing to their potential importance in societal transformations taking place in the Eastern Mediterranean at the end of the 3rd millennium BCE.

"Both pathogens, Y. pestis and S. enterica subsp. enterica, which were identified in this study at the site of Hagios Charalambos from this time of transition, can cause severe epidemics in human populations," the authors wrote.

"While it is unlikely that Y. pestis or S. enterica were the sole culprits responsible for the societal changes observed in the Mediterranean at the end of the 3rd millennium BCE," they added, "we propose that, given the [ancient DNA] evidence presented here, infectious diseases should be considered as an additional contributing factors; possibly in an interplay with those proposed before, such as climate and migration."