LONDON.- The earliest evidence of the plague in Britain has been discovered.

Researchers investigating Bronze Age human remains found in Somerset and Cumbria discovered the DNA of Yersinia pestis, the bacteria that causes the plague, inside three skeletons. As this DNA is very easily degraded, it’s also possible that other individuals may have been infected.

It’s not clear whether the three known victims were killed by plague or not, but this strain appears to lack virulence genes which later pandemic-causing bacteria would have.

Dr Pontus Skoglund, a co-author of the paper and the group leader of the Francis Crick Institute’s Ancient Genomics Laboratory, says, ’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.’

The findings of the study were published in the journal Nature Communications.

The origins of the plague

While there are over 20 species of bacteria in the Yersina family, only three are known to cause disease in humans. Both Y. enterocolitica and Y. pseudotuberculosis are food and water-borne diseases which cause diarrhoea-like symptoms and often aren’t serious.

This isn’t the case for Y. pestis, however. It causes three diseases, bubonic, septicaemic and pneumonic plague, all of which are very serious and can cause death without treatment by antibiotics.

Genetic studies have shown that the plague bacterium evolved from Y. pseudotuberculosis and gained genes that allowed it to infect fleas and other animal hosts while boosting its defences against their immune systems.

This took place at some point in the past 20,000 years, though it’s not known to have caused its first major pandemic until around 1,500 years ago.

This was the Justinian Plague, which is believed to have begun in Central Asia before spreading into the Mediterranean and Europe. While its severity is a matter of debate, it was certainly nowhere near as deadly as the second plague in fourteenth century Europe, better known as the Black Death.

This is thought to have been the deadliest pandemic ever, and is estimated to have killed around a third of Europe’s population at the time.

Its impacts were so pronounced that it caused social, economic and environmental changes, with a study published last year suggesting pollen levels dropped substantially in some areas as so many of the workers who tended crops died.

It was followed in the nineteenth and twentieth centuries by a smaller pandemic originating in China which subsequently spread around the world as global transport improved. It is this strain of the virus, known as Y. pestis orientalis, that is the main cause of sporadic outbreaks today.

While there are no records of any earlier pandemics, the genetic age of Y. pestis suggests that it was circulating for some time beforehand. Studies of human remains from Europe and Asia have found evidence of the disease from around 4,700 years ago, but it was only known to have reached as far west as Germany.

The new research, however, suggests that ancient migrations may have brought it as far as the UK.

An outbreak of violence

The researchers sampled teeth from 34 skeletons found at two British Bronze Age burial sites at Charterhouse Warren in Somerset and Levens Park in Cumbria. As teeth are very resistant to decay, the dental pulp contained within can preserve fragments of Y. pestis DNA left during an infection.

Two teeth from Chartehouse Warren, thought to be from children aged around 10 and 12, contained traces of plague, as did the tooth of a woman aged between 35 and 45 from Levens Park. While there is no evidence that the other skeletons contained Y. pestis DNA, the researchers can’t rule out other individuals may have had the disease too due to the difficulty in detecting its presence.

If other individuals did have the plague, it could help to solve a historical mystery at Charterhouse Warren. The 30 skeletons found here have all been dumped into a shaft in the rock, and show signs of trauma just before their death and dismemberment.

It’s possible that this group may have been attacked because they were suffering from the plague, with one of the infected children showing signs of trauma. Proving that the other skeletons at the site were also infected with plague could provide more evidence that this was the case.

The presence of distinctive Beaker pottery among the skeletons suggests that the strain found in Britain may have been brought to the island during ancient migrations around 4,400 years ago.

Using the Y. pestis DNA that has been extracted, the team were also able to sequence the genome of the bacteria. Their analysis revealed that this strain of plague lacked important genes, including ‘ymt’, which enhances the ability of plague to survive in, and spread using, fleas.

Samples of Y. pestis carrying the ymt gene are known from around 200 years after the British burials of this study, suggesting that Bronze Age Europe would have had a variety of different strains in circulation at the same time.

Pooja Swali, a PhD student at the Crick Institute who led the study, says, ’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.’