During the two World Wars, Bartonella quintana was responsible for trench fever and is now recognised as an agent of re-emerging infection. Many reports have indicated widespread B . quintana exposure since the 1990s. In order to evaluate its prevalence in ancient populations, we used real-time PCR to detect B . quintana DNA in 400 teeth collected from 145 individuals dating from the 1 st to 19 th centuries in nine archaeological sites, with the presence of negative controls. Fisher’s exact test was used to compare the prevalence of B . quintana in civil and military populations. B . quintana DNA was confirmed in a total of 28/145 (19.3%) individuals, comprising 78 citizens and 67 soldiers, 20.1% and 17.9% of which were positive for B . quintana bacteraemia, respectively. This study analysed previous studies on these ancient samples and showed that the presence of B . quintana infection followed the course of time in human history; a total of 14/15 sites from five European countries had a positive prevalence. The positive rate in soldiers was higher than those of civilians, with 20% and 18.8%, respectively, in the 18 th and 19 th centuries, but the difference in frequency was not significant. These results confirmed the role of dental pulp in diagnosing B . quintana bacteraemia in ancient populations and showed the incidence of B . quintana in both civilians and soldiers.

Ancient dental pulps are highly precious samples because they conserve DNA from humans and blood-borne pathogens for ages. However, little is known about the microbial communities present in dental pulps. Here, we analyzed ancient and modern dental pulp samples from different time periods and geographic regions and found that they are colonized by distinct microbial communities, which can be differentiated from other oral cavity samples. We found that despite the presence of environmental bacteria, ancient dental pulps conserve a clear and well-conserved record of oral microbes. We were able to detect several different oral pathogens in ancient and modern dental pulps, which are commonly associated with periodontal diseases. We thus showed that ancient dental pulps are not only valuable sources of DNA from humans and systemic infections, but also an open window for the study of ancient oral microbiomes.

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