Two recent studies have provided new genomic evidence about Yersinia pestis, the bacterium responsible for plague, including the sixth-century Plague of Justinian and the Black Death. The findings link archaeological remains to pathogen genomics and help clarify how plague spread and persisted across Eurasia.
The first study, published in Genes, examined a mass grave from Jerash, Jordan, dated to around 550-660 CE. The grave, located in an abandoned Roman hippodrome, contained more than 200 individuals. Researchers used proteomics and ancient DNA analysis to test teeth from several skeletons. They identified Y. pestis in five individuals, all carrying nearly identical strains. This indicates a single lineage was circulating at the time of the outbreak.
The Jerash strain grouped closely with other First Pandemic genomes but is the first recovered from the Eastern Mediterranean, near the historical epicenter of the Justinianic Plague. Genetic analysis showed the strain carried key virulence factors, such as Ymt, Pla, and the F1 capsule, which are linked to flea transmission and disease progression. Phylogenetic comparisons confirmed that the Jerash strain belonged to the same wider cluster as plague genomes recovered from Western Europe.
The second study, published in Pathogens, placed these findings in a global context. Researchers analyzed 326 Y. pestis genomes spanning prehistory to the present day, including 68 ancient samples. The results showed that plague pandemics did not come from one single strain, but instead emerged independently from multiple deep-rooted reservoirs in Eurasia.
Evidence from the Neolithic and Bronze Age demonstrated that Y. pestis was circulating long before recorded pandemics. Periods of rapid genetic change coincided with known outbreaks, while many modern strains showed little change over time, suggesting the bacterium often persists in animal or environmental reservoirs before re-emerging in humans.
A review of host associations revealed that ancient pandemic strains have so far only been found in humans, while modern strains are also detected in rodents, fleas, and soil. This points to differences in transmission: earlier pandemics may have been largely human-driven, while modern outbreaks often reflect spillovers from non-human reservoirs.
Together, the findings of both studies expand understanding of plague’s long history and show how laboratory techniques can connect past epidemics to present-day pathogen surveillance.
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