Ancient skeleton tests reveal how disease evolved

Researchers at the University of Bradford have taken part in analysis which has found how ancient DNA for a type of bacteria which causes a fever has evolved over thousands of years.

Borrelia recurrentis bacteria causes relapsing fever, an illness with many recurring episodes of fever, which is typically found today in areas with poor sanitation or overcrowding, such as refugee camps.

It is a distant cousin of the bacteria which causes Lyme disease.

Working with the Francis Crick Institute and UCL on samples of archaeological human bone, researchers believe the work can help show how diseases might develop and change in the future.

Four samples from across England tested positive for Borrelia recurrentis, caused by bacteria spread through the bites of lice rather than ticks.

The samples, dating back to the medieval and Iron Age periods, were obtained from the skeletons of infected people.

These included DNA from bone and teeth fragments from a female skeleton from Wetwang Slack, an Iron Age archaeological site in East Yorkshire, and fragments from remains found in Canterbury in Kent, Poulton in Cheshire and South Gloucestershire.

Scientists manged to sequence the whole genome, an organism's complete set of DNA, from the four samples.

Ranging from 2,300 to 600 years ago, their samples included the oldest Borrelia recurrentis genome to date.

The research found how the relapsing fever spread from lice to ticks which may have coincided with changes in human lifestyles, such as living closer together and the beginning of the wool trade.

Dr Jo Buckberry, from the University of Bradford's School of Archaeological and Forensic Sciences, said: "It's really exciting to work with ancient DNA specialists, to identify diseases than we cannot see on the skeleton.

"As we celebrate Bradford 2025 and reflect on our role in the historic wool trade, it's fascinating to know our archaeological research has contributed to the understanding of how the use of wool has changed the diseases affecting people in the past."

Researchers looked at differences in the ancient and modern-day Borrelia recurrentis and found the species likely diverged from its nearest tick-borne cousin, B.duttonii, about 4,000 to 6,000 years ago.

The study also found a change from the bacteria's transmission from ticks to lice happened during the transition from the Neolithic, or New Stone Age, period to the Early Bronze Age.

Pontus Skoglund, group leader of the Ancient Genomics Laboratory at the Francis Crick Institute, said: "Understanding how bacteria such as Borrelia recurrentis became more severe in the past may help us understand how diseases could change in the future.

"The time points we've identified suggest that changes in human societies such as new clothing material or living in larger groups may have allowed Borrelia recurrentis to jump vectors and become more lethal, an example of how pathogens and humans have co-evolved."

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