The plague, caused by the bacterium Yersinia pestis, is a fearsome disease that affects humans and other mammals. In humans, it usually appears after someone is bitten by an infected rodent flea or after handling an animal infected with the disease.
Although today modern antibiotics have pretty much contained the disease, the plague is infamous for killing millions of people in Europe during the Middle Ages. However, human plague infections do continue to occur in this day and age in rural areas in the western United States, in Africa, and in Asia.
So far, gene sequencing has revealed that the plague (in particular the one responsible for the Black Death which caused about 100 million deaths around the world roughly between 1348 and 1350) originated in China over 2000 years ago. However, the new discovery of a hunter-gatherer's skull who lived in Europe over 5,000 years ago may change our estimates of when the devastating plague first appeared.
The skull contains the oldest known traces of the bacteria responsible for causing the plague. The discovery came as a surprise to the scientists who were merely looking for any leftover DNA traces.
Their analysis included screening for potential pathogens and that’s when they spotted the bacteria's proteins allowing them to reconstruct this old genome of the Yersinia pestis strain that they dubbed RV 2039.
Scientists have long believed that Yersinia pestis originated from another species of bacteria called Yersinia pseudotuberculosis and that it essentially split off of this bacteria. Now, the new study's authors are arguing that the skull may indicate that this split occurred further back (about 7,000 years ago) and that this original version of the plague was tamer and less contagious than the one responsible for the Black Death.
"The genomic and phylogenetic characteristics of RV 2039 are consistent with the hypothesis that this very early Y. pestis form was most likely less transmissible and maybe even less virulent than later strains," wrote the study's authors. The strain would have transformed over time into the devastating version that grew to be known as the Black Death.
The study was published in Cell Reports.