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People were infected with the plague pathogen 5000 years ago. Researchers from Kiel identified the genetic material of the Yersinia pestis bacterium in a man who at that time lived in what is now Latvia. The researchers write that there were probably no major plague epidemics such as those in late antiquity or the Middle Ages in the trade magazine Cell Reports. The man was probably infected by an animal bite, but the pathogen was probably less contagious than later strains.
The team led by Julian Susat and Ben Krause-Kyora from the University of Kiel examined the bones of a total of four people who had been buried in Latvia near the Salaca River. The archaeological site known today as Rinnukalns consists of layers of freshwater mussels and fish bones that were deposited over 5000 years ago in a short period of 100 to 200 years.
The plague strain differs from later pathogens from the Bronze Age
The amateur archaeologist Carl Georg von Sievers discovered bone fragments from two people as early as 1875. It was a 12 to 18 year old woman and a 50 year old man who the archaeologist classified as “prehistoric”. To confirm this assumption, he sent the skulls to the physician Rudolf Virchow in Berlin, who examined them. After the Second World War, the bones were lost; they were only found in a Virchow collection in 2011.
In these and in the bones of two other people discovered in Rinnukalns, an adult male and a newborn, the researchers now looked for genetic traces of pathogens. They found what they were looking for in the 50-year-old man, known as RV2039: They discovered DNA from Yersinia pestis, the plague pathogen. The proven strain is genetically different from later strains of the Neolithic and Bronze Age, the researchers report.
Their analyzes showed that Yersinia pestis split off from the bacterium Yersinia pseudotuberculosis around 7000 years ago – earlier than previously assumed. About 5000 years ago the line of the plague pathogen began to fan out into several tribes. The pathogen found in RV2939 is the first of these strains.
The pathogen has not yet been spread via fleas
It is conceivable that people at the time were infected by rodents that they hunted. In Rinnukalns, the remains of beavers were found that were known to be frequently infected with Y. pseudotuberculosis, the predecessor of the now proven plague pathogen.
The researchers write that it is unclear whether and how much people suffered from the plague. The pathogen still lacked the genetic adaptation for transmission via fleas, as is the case with bubonic plague. However, theoretically it was able to migrate into the lungs and then be carried on with aerosols. The pulmonary plague is rare today – as it was probably back then, the researchers write.
It is difficult to assess the danger and infectivity of the early pathogens. So far, evidence of the bacterium in prehistoric people has always been isolated. It is therefore conceivable that the man suffered from the so-called septicemic plague, in which the pathogen is transmitted through animal bites and then spreads in the bloodstream.
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