Genomic blueprint of a relapsing fever pathogen in 15th century Scandinavia.. 15th-century LBRF

Louse-borne relapsing fever (LBRF) is known to have killed millions of people over the course of European history and remains a major cause of mortality in parts of the world. Its pathogen, Borrelia recurrentis, shares a common vector with global killers, such as typhus and plague, and is known for its involvement in devastating historical epidemics, such as the Irish Potato Famine. Here, we describe a European and historical genome of B. recurrentis, recovered from a 15th-century skeleton from Oslo, Norway. Our distinct European lineage has a discrete genomic makeup, showcasing an ancestral oppA-1 gene and gene loss in antigenic variation sites. Our results illustrate the potential of ancient DNA research to elucidate dynamics of reductive evolution in a specialised human pathogen and to uncover aspects of human health usually invisible to the archaeological record.