Levens ring cairn where plague DNA was found

Francis Crick Institute researchers have found three ancient cases of Yersinia pestis, the bacteria that causes the plague, in Britain. This is the oldest evidence of the plague in Britain.

The team worked with the University of Oxford, the Levens Local History Group, and the Wells and Mendip Museum to identify two cases of Yersinia pestis in human remains from a mass burial in Charterhouse Warren in Somerset and one in a ring cairn monument in Levens in Cumbria. They took small skeletal samples from 34 individuals in the two sites and screened for the presence of Yersinia pestis in teeth. This process involves drilling into the tooth and extracting dental pulp to find DNA remnants of infectious diseases.

The DNA was analyzed and three cases of Yersinia pestis were identified: two children estimated to be between 10-12 years old when they died, and one woman aged between 35-45. Radiocarbon dating showed that the three people likely lived at about the same time.

The plague has been identified in several individuals from Eurasia between 5,000 and 2,500 years before present (BP), a period spanning the Late Neolithic and Bronze Age (termed LNBA). However, it had not been seen before in Britain at this point in time. The wide geographic spread suggests that this strain of the plague may have been easily transmitted.

The researchers used genome sequencing to demonstrate that this strain of Yersinia pestis closely resembles the strain found in Eurasia during the same period. All of the identified individuals lacked the yapC and ymt genes, which are present in later strains of plague. The ymt gene is known to be essential in transmitting the plague through fleas. Based on this information, it is believed that this strain of the plague was not transmitted through fleas, unlike later strains such as the one that caused the Black Death.

Pathogenic DNA, which refers to DNA from bacteria, protozoa, or viruses that cause disease, degrades quickly in incomplete or eroded samples. Therefore, it is possible that other individuals at these burial sites were also infected with the same strain of plague.

The Charterhouse Warren site is unique because it differs from other funeral sites from the same time period; the individuals buried there appear to have died from trauma. The researchers speculate that the mass burial was not due to an outbreak of plague but rather that the individuals may have been infected at the time of their death.

Pooja Swali, first author and PhD student at the Crick, 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.”

Pontus Skoglund, group leader of the Ancient Genomics Laboratory at the Crick, said,

“This research is a new piece of the puzzle in our understanding of the ancient genomic record of pathogens and humans, and how we co-evolved.

“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. Future research will do more to understand how our genomes responded to such diseases in the past, and the evolutionary arms race with the pathogens themselves, which can help us to understand the impact of diseases in the present or in the future.”