Oldest strain of deadly infection discovered in ancient skull

Scientists have found the oldest strain of the plague bacillus, Yersinia pestis, in the remains of a hunter-gatherer 5,000 years ago. Genetic analysis showed that the ancestor of the plague pathogen that caused the Black Death pandemic in the Middle Ages was less contagious and less deadly at first, Cell Reports noted.

The remains, designated RV 2039, belonged to a man 20-30 years old. The remains of three more people were also found at the burial site. All four most likely belonged to the same hunter-gatherer group.

The researchers examined samples of dental tissue and skull bones from all four people, and then tested for the presence of bacterial and viral pathogens. They identified the genetic material of Y. pestis inside the bones of RV 2039 and then reconstructed the bacterial genome and compared it with the genomes of other ancient strains. As it turns out, the plague stick is part of a lineage that originated 7,000 years ago.

The early strain is missing several genes characteristic of the variant that caused the medieval pandemic, which claimed the lives of half of the population of Europe. For example, it lacks a gene that promotes the transfer of a microorganism from fleas to humans and the formation of buboes in sick people with the bubonic form of the disease. This type of flea transfer also requires the death of the host human, after which the insects begin to spread to other people, spreading the pathogen. This plague adaptation took over 1,000 years to develop.

Scientists don't know what symptoms RV 2039 had, but most likely it died from a bacterial infection. Other people who were buried with him showed no signs of infection, indicating that the plague bacillus most likely was not transmitted by airborne droplets. Most likely, RV 2039 became infected through a rodent bite.

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