What pathogens were behind the epidemics that were commonly referred to as “pestilence” in the late Middle Ages? In the case of the dead in a mass grave in the Hanseatic city of Lübeck, analyzes of microbial DNA residues now show that they were not carried away by plague bacteria, but by particularly aggressive salmonella, which cause a disease known as paratyphoid fever.
The terrible epidemics are almost a trademark of the late Middle Ages: Europe was ravaged by sometimes devastating epidemics, which in historical texts were usually generally referred to as “pestis” or “pestilentiae”. The worst hit was the so-called Black Death, which spread between 1346 and 1353 in all major cities in Europe and claimed millions of victims. It is now accepted that this disease was caused by the bacterium Yersinia pestis. In other cases, however, it is unclear which pathogens were actually behind the infectious diseases known as “pestilence”. This also applies to some late medieval epidemics in the Hanseatic city of Lübeck. In the city chronicles in the 14th century alone there is talk of at least six “pestilences”, the causes of which are considered unclear.
Tracking down pathogens
An interdisciplinary research team from the Christian-Albrechts-Universität zu Kiel has now devoted itself to researching epidemics in medieval Lübeck. Specifically, they dealt with archaeological traces that had already come to light in the early 1990s: mass burials were discovered during renovations at the old Heiligen-Geist-Hospital in Lübeck. Spread over various pits of various sizes, a total of more than 800 skeletons of all genders and ages were recovered, which were dated to the second half of the 14th century.
These findings and the high number of people who apparently died within a short period of time indicated an infectious disease as the cause of death. At first it was suggested that they were victims of the plague. But the scientists now wanted to know more precisely. As part of their study, they isolated, sequenced and analyzed DNA remains from samples from a total of 92 skeletons. The hope was to come across traces of the genetic material of the pathogens that had once become human’s undoing.
Aggressive salmonella detected
In the case of dead people from two pits, this was successful: the scientists were able to detect the genetic material of the bacterium Salmonella enterica with the subspecies enterica Paratyphi C. This is the causative agent of the so-called paratyphoid. The bacteria can spread quickly and find their way into the human body through consumption of contaminated water or food. The infection manifests itself as a persistent high fever, abdominal pain, nausea and diarrhea. If left untreated, the disease can be life-threatening: To this day, paratyphoid fever continues to claim fatalities in some parts of the world. Apparently this was also the case in Lübeck in the Middle Ages: “We know from the city’s chronicles that there was a ‘Pestilencia’ recorded for the year 1367, which claimed many lives, but was limited to Lübeck,” says co-author Gerhard Fouquet . According to the scientists, it is obvious that the dead from the mass burial at the Holy Spirit Hospital were victims of this “pestilence” – which, according to the results, was an outbreak of paratyphoid fever.
The molecular biologists on the research team also succeeded in fully reconstructing three of the paratyphoid C genomes. This enabled them to compare it with the genetic material of a previously found pathogen from Norway, which dates from around 1200. “Our analyzes indicate a high degree of relationship between the paratyphoid C strains that occurred in the Middle Ages,” says first author Magdalena Haller. It is therefore obvious that the pathogen spread via the trade routes at the time. The analyzes thus provide information about the evolution and spread of the paratyphoid pathogen, the origin of which is still little known, the scientists write.
In conclusion, Haller says: “Paratyphoid C actually does not occur in Europe anymore. However, our results indicate that the pathogen was quite common in the past. Recurring outbreaks of paratyphoid fever must have frightened people back then, ”says the researcher.
Source: Christian-Albrechts-Universität zu Kiel, specialist article: iScience, doi: 10.1016 / j.isci.2021.102419