Research team uses ancient DNA to gain insight into the development and history of epidemics in historical Lübeck
A team of researchers at Kiel University (Christian-Albrechts-Universität, CAU), Germany, gained insights into the development and history of epidemics in historical Lübeck by means of ancient DNA (aDNA) analysis.
In the Late Middle Ages, urban Europe often fell victim to rampant epidemics. Local disease outbreaks as well as global pandemics were increasingly described in historical sources. Perhaps the most notorious epidemic in human history was the plague, caused by the bacterium Yersinia pestis, which spread throughout Europe's major cities between 1346 and 1353 CE. It became known as the "Black Death". Two-thirds of the European population succumbed to the disease. Thus, the plague has become the eponym for the expression "pestis" or "pestilentiae", which was often used in historical records to describe disastrous epidemics of unknown cause. Also Lübeck was struck by at least six "pestilences" in the 14th century alone, as recorded in the city chronicles. To date, there is no evidence of the pathogens responsible for these diseases.
During construction work at the Holy-Ghost-Hospital (Heiligen-Geist-Hospital) in Lübeck in the early 1990s, several mass burials were discovered next to the outer hospital walls. Scattered over various pits of different sizes, a total of more than 800 skeletons of all sexes and ages were recovered from the site. The pits could be dated to the second half of the 14th century using the radiocarbon dating technique. The large number of people who had died within a short period of time without signs of violence suggested an infectious disease as the cause of death.
Salmonella identified as the trigger
An interdisciplinary team led by Prof. Ben Krause-Kyora from the Institute of Clinical Molecular Biology (IKMB) at CAU has been investigating the cause of death for the people in the mass graves. For this purpose, the aDNA from a total of 92 skeletons was isolated, sequenced and analyzed. "Our initial aim was to determine whether it is at all possible to use aDNA analyses to identify the pathogen responsible for this unknown epidemic," emphasizes Prof. Almut Nebel, also affiliated with the IKMB. "Being able to successfully demonstrate this is an important methodological milestone." The team was able to detect the bacterial pathogen Salmonella enterica subsp. enterica Paratyphi C in the human remains from two pits. "From the city chronicles we know that for the year 1367 CE an unknown "pestilentia" is recorded, which claimed many lives among all social strata, but was confined to Lübeck only", remarks Prof. Gerhard Fouquet from the Historical Seminar at Kiel University. This finding provided the researchers with the earliest evidence to date of an epidemic caused by Salmonella.
S. Paratyphi C is an invasive Salmonella species. The causative agent spreads rapidly and is transmitted to the human host via the consumption of contaminated water or food. Once contracted, the disease manifests itself as continued high fever, abdominal pain and nausea, at times also diarrhea. Without medical treatment, the disease course can be fatal.
The molecular biologists from Kiel further succeeded in fully reconstructing three of the S. Paratyphi C genomes. "Our results indicate a close relationship among the Paratyphi C strains in the Middle Ages," explains first author Magdalena Haller. It can be assumed that the pathogen has spread along commercial routes of the time, including those of the Hanseatic League. The analyses thus provide insights into the origin and evolution of the bacterium S. paratyphi, about which little is yet known. "Paratyphi C is virtually absent from Europe today. However, our results suggest that the pathogen was fairly common in the past. Recurrent outbreaks of paratyphoid fever must have severely affected people back then," explains Haller.
The Lübeck mass burial site represents a unique scientific resource for the study of past epidemics. "Through the close cooperation of molecular biology, history and archaeology, we have not only opened a door to the Middle Ages, but also built a bridge to our Corona era", emphasizes Dr. Dirk Rieger, head of the department of archaeology of the Hanseatic City of Lübeck.
The results of the study were recently published in the international journal iScience. The study was supported by the Collaborative Research Centre 1266 "Scales of Transformation“, the Cluster of Excellence ROOTS, and research funding from the CAU Medical Faculty.
Haller, M., Callan, K., Susat, J., Flux, A., Immel, A., Franke, A., Herbig, A., Krause, J., Kupczok, A., Fouquet, G., Hummel, S., Rieger, D., Nebel, A., Krause-Kyora, B. (2021) Mass burial genomics reveals outbreak of enteric paratyphoid fever in the Late Medieval trade city Lübeck. iScience 24, 102419.