EVIDENCE of the oldest plague casualties in Britain has been discovered in Somerset.

Researchers have identified three 4,000-year-old British cases of Yersinia pestis, the bacteria causing the plague.

Two cases of Yersinia pestis were identified in human remains found in a mass burial at Charterhouse Warren and in a ring cairn monument at Levens, Cumbria.

Researchers took skeletal samples from 34 individuals across the two sites, screening for the presence of Yersinia pestis in teeth.

They analysed the DNA and identified three cases of Yersinia pestis in two children estimated to be between 10- and 12-years-old and a woman aged between 35 and 45.

The plague has previously been identified in human remains from Eurasia between 5,000 and 2,500 years ago, a period spanning the Late Neolithic and Bronze Age, but not previously in Britain.

Using genome sequencing, researchers from London's Francis Crick Institute and colleagues from Oxford University, the Levens Local History Group and the Wells and Mendip Museum showed the particular strain of the Yersinia pestis looks very similar to the strain identified in Eurasia at the same time.

The individuals identified all lacked the yapC and ymt genes seen in later strains of plague.

Study author Pooja Swali said because pathogenic DNA from bacteria, protozoa, or viruses which cause disease degrades quickly in samples which might be incomplete or eroded, it’s possible that other people at the burial sites may have been infected with the same strain.

The Charterhouse Warren site is rare as it doesn’t match other funeral sites from the time period – those buried there appear to have died from trauma.

The researchers believe the mass burial wasn’t due to an outbreak of plague, but individuals may have been infected at the time they died.

Ms Swali, a PhD student at the Crick Institute, said: "The ability to detect ancient pathogens from degraded samples, from thousands of years ago, is incredible.

"These genomes can inform us of the spread and evolutionary changes of pathogens in the past, and hopefully help us understand which genes may be important in the spread of infectious diseases.

"We see that this Yersinia pestis lineage, including genomes from this study, loses genes over time, a pattern that has emerged with later epidemics caused by the same pathogen.”

Dr Pontus Skoglund, group leader of the Ancient Genomics Laboratory at the Crick Institute, said: “We understand the huge impact of many historical plague outbreaks, such as the Black Death, on human societies and health, but ancient DNA can document infectious disease much further into the past."

The findings were published in the journal Nature Communications.