Researchers have identified the oldest cases of plague in Britain to date, with DNA that is 4,000 years old.

The team from the Francis Crick Institute in London has found three ancient British cases of Yersinia pestis -- the bacteria that causes the plague -- in skeleton samples of two children and one woman.

Two of the cases were found in a mass burial site in Charterhouse Warren in Somerset. The third was discovered in a ring cairn monument in Levens in Cumbria after researchers took skeletal samples of teeth from 34 people at the two sites.

The scientists drilled into the teeth and extracted dental pulp, which can trap DNA remnants of infectious diseases. They then analyzed DNA and found Yersinia pestis in the two children, who were ages 10 to 12, and the woman, who died around age 34 or 35.

Radiocarbon dating showed it’s likely the three people lived at roughly the same time.

While the plague had been previously identified in people from Eurasia between 5,000 and 2,500 years ago, it had not been seen in Britain at this point in time.

Researchers noted that the wide geographic spread suggests this strain of the plague may have been easily transmitted.

This strain of the plague is the LNBA lineage, for the Late Neolithic and Bronze Age, and was likely brought into Central and Western Europe around 4,800 years ago by humans expanding into Eurasia. This research now suggests it extended into Britain.

It looks very similar to the strain identified in Eurasia at this time, according to genome sequencing, the researchers said.