Difficult times are on the horizon: the rural population of southern Germany was evidently weakened in the early Middle Ages and suffered primarily from various infectious diseases. This emerges from DNA traces of pathogens and the characteristics of around 1300-year-old skeletons from a Merovingian settlement in today's Baden-Württemberg. Poor human condition and high infection rates may have been linked to worsening climate during this era, the scientists say.
The Middle Ages are often associated with misery and disease. However, this refers more to the late Middle Ages, which were plagued by the plague: most of the knowledge about pathogens and epidemics refers to this era after the 12th century AD. In contrast, the health situation and the course of infection in the early Middle Ages are still largely unknown. A research team led by Joanna Bonczarowska from the Christian-Albrechts-University in Kiel (CAU) has now devoted itself to this topic.
In order to track down former pathogens, they used the method of DNA analysis in the case of human remains that were discovered near Lauchheim in the East Württemberg region. They come from graves of the 7th to 8th centuries AD, which were near the homesteads of a rural settlement. "The dating of the graves indicates that the burial ground was used for about a century, i.e. three to four generations," says Bonczarowska. The researchers managed to isolate DNA from 70 skeletons. They were then able to subject this genetic material to a so-called metagenomic analysis. This means they looked for traces of the genetic material of pathogens in the DNA obtained.
Traces of various pathogens
"The analysis results show that the residents suffered from infections with various pathogens, including Mycobacterium leprae, the hepatitis B virus, the parvovirus B19 and the variola virus VARV," reports senior author Ben Krause-Kyora from the CAU. These pathogens are known to cause both chronic and acute diseases of varying degrees of severity, the researchers explain. M. leprae is the causative agent of the notorious leprosy that has long afflicted people in Europe. In addition to abdominal pain and fever, hepatitis B virus infections can cause severe liver disease, and parvovirus B19 is the causative agent of ringworm.
Particularly noteworthy, according to the researchers, is the trace of the variola virus, which until it was eradicated in 1980 caused smallpox that claimed many lives. "Due to the genetic differences between modern and medieval VARV, however, we cannot say what the symptoms of the infection looked like in the Middle Ages and whether the pathogen was as dangerous as the more modern variola virus," says Krause-Kyora.
Severe contamination and multiple infections
Overall, the researchers were able to identify genetic traces of at least one of the pathogens in 31 percent of the individuals examined. In addition, they also found a significant number of co-infections with two or even three different pathogens. According to the researchers, the findings reflect a high level of infection - and there is probably also a considerable number of unreported cases: "Once all soft tissue has been destroyed, only blood-borne pathogens can be reliably detected in the bones. Considering this limitation along with the degradation of DNA molecules that occurs over time, some infections may have gone undetected," says Krause-Kyora.
As the team further reports, the characteristics of the bones also revealed a generally poor state of health of the early medieval residents of Lauchheim: their skeletons showed signs of malnutrition in addition to traces of diseases. Co-author Almut Nebel from the CAU says about the possible background. “At that time, Europe was experiencing a rapid climatic decline known as the Late Antique Little Ice Age. Such changes can lead to crop failure and eventually famine.” This may also have been linked to the high rates of infection: “In theory, a famine would debilitate the malnourished population and facilitate the spread of pathogens in the community. These people were in very poor health, and the conditions seemed conducive to the spread of disease and the development of pathogens," Nebel concludes.
Source: Christian-Albrechts-University of Kiel, specialist article: Genome Biology, doi: 10.1186/s13059-022-02806-8