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The bacterium Yersinia pestis that causes the plague is dated to have appeared thousands of years before the 3 pandemics

The bacterium Yersinia pestis that causes the plague is dated to have appeared

Scientists have found evidence suggesting that historic plague pandemics, such as the Black Death, were not caused by newly evolved bacteria, but by ones that may have appeared many centuries before their outbreak.

The bacterium Yersinia pestis that causes the plague is dated to first appearing in humans about 5,000 years ago, and through animals and trade routes, Y. pestis spread globally over time, according to a study published Thursday in the journal Communications Biology .

It caused the first plague pandemic in the sixth to eighth centuries and the second in the 14th to 19th centuries. The bacterium also caused the third plague pandemic between the 19th and 20th centuries.

By collecting 601 Y. pestis genome sequences, including modern and ancient strains, researchers from Canada and Australia were able to calculate when bacterial strains might emerge as a threat. They separated the different strains of plague bacteria and analyzed each population individually.

The strain responsible for the Black Death, which the study says is thought to have started in 1346, was estimated to have evolved from a type of virus between 1214 and 1315.

The strain of Y. pestis associated with the first plague pandemic first appeared during the Plague of Justinian, which began in 541. However, researchers estimated that the strain was already present between 272 and 465—until almost 270 years before the explosion.

"It shows that any major plague pandemic likely occurred many decades to centuries earlier than the historical record suggests," study co-author and evolutionary geneticist Hendrik Poinar told CNN.

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