Scientists have discovered the earliest known traces of plague, dating back about 5,500 years, around 200 years earlier than previously believed. The study results were published in the journal Nature.

The research was conducted by an international team of scientists led by evolutionary geneticist Eske Willerslev of the University of Copenhagen. They analyzed ancient remains from four burials in the Lake Baikal region of Siberia and identified fragments of plague pathogen DNA in the teeth of 18 ancient hunter-gatherers.

Radiocarbon analysis showed that the infection may have caused two waves of outbreaks: the first dates to about 5,500 years ago. According to the researchers, the ancient form of the disease was in the early stages of evolution and spread among small groups of people.

Scientists suggest that infection may have occurred through contact with infected marmots — through the consumption of raw meat or the processing of hides, as well as via airborne transmission between people.

Children aged 8 to 11 were especially common among the victims. In some burials, close relatives were found buried together, which, according to the researchers, points to local outbreaks of infection in small communities.

The authors note that the ancient form of plague existed long before the bubonic form that caused the Black Death pandemic in the 14th century, yet even then it may have led to significant mortality even in small nomadic groups.

According to the researchers, studying the early evolution of plague helps better understand how pathogens become dangerous to humans and how new pandemic threats may emerge in the future.