Molecular evidence for the etiologic agent of the Tyrolean epidemic of 1636

O. Kersten1, M. Guellil1, S. Luciani2, I. Marota2, B. Bramanti1 1University of Oslo, Department of Biosciences, CEES, Oslo, Norway 2University of Camerino, Camerino, Italy Containing major, historical and modern, trans-alpine travel routes, the region of Tyrol has been affected by various epidemics in the past. In August 1636, the Tyrolean village of Naturns (Italy) was struck by a disease referred to as "pest", killing up to 25% of the local population and leading to an increase of burials in the so-called "plague graveyard" of the St. Procolo church on the outskirts of the village. While historical sources indicated that the outbreak was likely a typhus epidemic caused by the bacterium Rickettsia prowazekii and not plague and its bacterial pathogen, Yersinia pestis, molecular evidence for the etiologic agent of this event was missing. To clarify the nature and cause of the outbreaks striking Tyrol in the 17th century, we attempted to identify the pathogen responsible for the epidemic by investigating tooth samples from individuals recovered from multiple burials in the graveyard of the St. Procolo church in Naturns dated to 1636. Human ancient DNA (aDNA) content in teeth from 24 individuals was assessed by quantitative PCR (qPCR). All extracts were screened for the presence of R. prowazekii and Y. pestis via PCR and qPCR, respectively, and samples exhibiting amplifications were further investigated via shotgun sequencing and metagenomic profiles. All teeth (24/24) contained sufficient endogenous DNA for the amplification of the human mitochondrial HVR1 region. qPCR results revealed the presence of Y. pestis pla and caf1 DNA in seven individuals, but no R. prowazekii DNA was detected in any of the 24 teeth over the course of the experiment. The metagenomic analyses are still undergoing. Contrary to historical evidence, which had suggested that the buried individuals had died of epidemic typhus, we have provided clear molecular evidence that the disease having struck Naturns in 1636 was, in fact, plague. Hence, the results of this study have shedded light on the historical past of Naturns and the Tyrolean region in the 17th century, and highlighted the importance of cooperation between archaeologists, historians, and molecular biologists in order to reconstruct the nature of ancient epidemics.