Fever-Causing Bacteria: Here's How They Evolved

Ancient DNA extracted from bones and teeth of people who lived in Britain hundreds and even thousands of years ago, between 2,300 and 600 years ago, can tell us about the evolution of some of the bacteria that cause fever and how it is closely linked to changes in human lifestyles, starting with the spread of woolen clothes and more crowded settlements, which made it easier to transmit from person to person.

This is revealed by a study published in the journal Science , led by University College London and the British Francis Crick Institute, which highlights the importance of ancient DNA in shedding light on the origin of infectious diseases.

Researchers led by Pontus Skoglund of the Francis Crick and Lucy van Dorp of University College London have sequenced the entire genomes of four ancient samples of Borrelia recurrentis , a bacterium that causes a relapsing fever disease that is now typically found in areas with poor sanitation or overcrowding, such as refugee camps. The samples come from human remains that are between 2,300 and 600 years old, meaning they have produced the oldest B. recurrentis genome to date.

The authors of the study then compared the DNA thus obtained with that of the modern bacterium, discovering that this species differentiated from its closest cousin between 6,000 and 4,000 years ago: the new evolutionary path undertaken has allowed B. recurrentis to change the animal with which it is transmitted: no longer ticks, but lice, more effective in spreading the bacterium among humans. This turning point coincides precisely with important changes in lifestyles, including the spread of wool fabrics, which offers better conditions for the deposition of lice eggs.

"Ancient DNA can improve our understanding of important but poorly studied diseases, such as relapsing fever," Skoglund says. "Understanding how bacteria like B.

recurrentis became more dangerous in the past can help us understand how diseases might evolve in the future. Our data - continues Skoglund - suggest that changes in human societies, such as the use of new clothing materials or living in larger groups, may have allowed B. recurrentis to become more lethal, an example of how pathogens and humans co-evolved."