Plague has been a human scourge for more than twice as long as had previously been thought, new research suggests.

Scientists say Yersinia pestis bacteria were infecting people in Eurasia at least 3,000 years before causing their first known pandemic, the Plague of Justinian, in 541 AD.

Ancestral plague would have been mostly spread by human-to-human contact, it is believed.

Later mutations occurring near the turn of the first millennium BC gave rise to the bubonic form of the plague spread by fleas and rats. Bubonic plague went on to decimate global populations in pandemics such as the Black Death, which wiped out half the population of Europe in the 14th century.

Y. pestis infection in humans may have emerged around the beginning of the Bronze Age, more than 5,000 years ago, according to the new evidence reported in the journal Cell.

Lead scientist Professor Eske Willerslev, from Cambridge University, said: “We found that the Y. pestis lineage originated and was widespread much earlier than previously thought, and we narrowed the time window as to when and how it developed.

“The underlying mechanisms that facilitated the evolution of Y. pestis are present even today. Learning from the past may help us understand how future pathogens may arise and evolve.”

The scientists analysed ancient DNA extracted from the teeth of 101 adults dating from the Bronze Age, who lived across the Eurasian land mass from Siberia to Poland. Y. pestis bacteria was identified in the DNA taken from seven individuals, the oldest of whom died 5,783 years ago.

Previously, direct molecular evidence for Y. pestis had not been obtained from a skeleton more than 1,500 years old.

Six of the samples were missing two key genetic components found in most modern strains of plague.

One of these components, ymt, allowed the bacteria to multiply in the guts of fleas until their host’s digestive tract is choked, leading the starving fleas to bite anything they could, thus spreading the disease.

Another mutation in a gene called pla helped the bugs spread across different tissues, turning a localised lung condition into a “bubonic” infection of the blood and lymph nodes.

Bronze Age plague was likely to have been the “pneumonic” form which causes hacking coughing fits before death.

High levels of migration at this time probably contributed to its spread, according to co-author Dr Marta Mirazon-Lahr, also from Cambridge University.

She said: “Well-documented cases have shown the pneumonic plague’s chain of infection can go from a single hunter or herder to ravaging an entire community in two to three days.”