Scientists have identified a strain of Yersinia pestis bacterium from the unearthed bones of a Neolithic woman in a burial site in Sweden.

A team of international researchers believes that the bones were around 4,500 years old, making the strain the oldest that has been identified in history. The team also claims that the strain is the closest to the genetic origin of the plague that they have ever seen.

Details of the discovery were published in the journal Cell.

The Most Ancient Case Of Plague

Y. pestis has wiped out large numbers of humans in history. In 541 CE, the Plague of Justinian caused the death of 25 million to 50 million, affected much of the Mediterranean.

The next major pandemic, the Black Death or the Great Plague, started in 1334 in China and spread to Europe, claiming an estimated 7 million to 200 million people. The Third Pandemic or the "Modern Plague" happened in 1855 and killed 12 million people in India and China.

"Plague is maybe one of the deadliest bacteria that has ever existed for humans. And if you think of the word 'plague,' it can mean this infection by Y. pestis, but because of the trauma plague has caused in our history, it's also come to refer more generally to any epidemic," explained Simon Rasmussen, from the Technical University of Denmark, and the senior author of the study.

The team of researchers wanted to study the evolution of the plague so they screened for sequences similar to modern strains of plague from genetic data of ancient humans. They found a strain they have never seen before in a 20-year-old woman who died about 5,000 years ago. Traces of the strain in the bones of another individual in the same burial site is proof that the woman died of the disease.

Tracing Back The History Of The Plague

The researchers believe that the plague diverged from another strain found from 5,700 years ago. Meanwhile, the ancestor of the strains in existence today and a plague that was common during the Bronze age diverged around 5,100 and 5,300 years ago. By the end of the Neolithic period, there were multiple strains of plague in existence.

The researchers also theorized that the plague spread when Eurasians invaded the area and displaced the Neolithic European settlements.

"These mega-settlements were the largest settlements in Europe at that time, ten times bigger than anything else," added Rasmussen. "They had people, animals, and stored food close together, and, likely, very poor sanitation."

The findings of the study are not definitive, but the researchers believe that it is a step forward to understanding how pathogens evolve to become extremely virulent and deadly.

ⓒ 2018 TECHTIMES.com All rights reserved. Do not reproduce without permission.