In an early medieval settlement, dangerous pathogens lurked around every corner

In an early medieval settlement, dangerous pathogens lurked around every corner

Skull from grave 83 in Lauchheim “Mittelhofen”. The team was able to detect three infections in this person. Photo credit: Isabelle Jasch-Boley

The analysis of DNA from 1,300-year-old skeletons made it possible to reconstruct the state of health of the Merovingian community in Lauchheim-Mittelhofen in modern-day Baden-Württemberg.

The study, published today in the journal genomic biology, shows a high prevalence of infection with various pathogens. The results also allow general conclusions to be drawn about the susceptibility to infections in times of climate change.

Poor personal hygiene, disease-carrying rats and generally unhygienic living conditions – the Middle Ages are generally regarded as the age of ubiquitous diseases. Most of what we know about medieval epidemics, however, relates to the late Middle Ages after the 12th century AD. In contrast, the course of infection in the early Middle Ages and the pathogens responsible for disease outbreaks during this period are still largely unexplored.

An interdisciplinary research team led by scientists from the University of Kiel (CAU) has now found evidence of a high prevalence of infectious diseases in the early medieval settlement of Lauchheim “Mittelhofen” (Baden-Württemberg) using the latest analysis techniques for ancient DNA.

The analysis shows various pathogens in the skeletons

For this study of the early medieval settlement of Lauchheim “Mittelhofen,” researchers isolated DNA from 70 human skeletons excavated within its boundaries. The tombs could be associated with distinguishable homesteads and dated to the late Merovingian period (7th–8th centuries AD).

“The DNA data showed that the residents of Lauchheim suffered from infections with various pathogens, such as Mycobacterium leprae, the hepatitis B virus HBV, the parvovirus B19 and the variola virus VARV,” says Professor Ben Krause Kyora from the Institute for Clinical Sciences Molecular Biology at the CAU and member of the ROOTS Cluster of Excellence, who led the research team.

The infectious agents detected in Lauchheim cause both chronic and acute diseases of varying degrees of severity. Infection with M. leprae can lead to the development of persistent and severely debilitating leprosy. The symptoms of an HBV infection range from mild abdominal pain and fever to liver fibrosis and liver cancer. B19 appears to be less dangerous because infection is usually asymptomatic and serious complications are rare. In contrast, before its eradication in 1980, the variola virus caused smallpox – an acute disease with high mortality.

“Due to the genetic differences between modern and medieval VARV, however, we cannot say what symptoms the infection had in the Middle Ages and whether the pathogen was just as dangerous as modern variola,” explains Prof. Krause-Kyora.

Many people even suffered from multiple infections

The authors found a significant number of co-infections with two or even three different infectious agents. Overall, 31% of the population with a molecular trace of infection with at least one pathogen died. “Although this figure is very high, it does not reflect the burden of disease at any given point in time. Dating of the graves suggests that the burial site was in use for around a century, i.e. between three and four generations. It’s important to keep this in mind,” says one of the first authors of the study, Joanna Bonczarowska from the Institute for Clinical Molecular Biology at the CAU.

Still, the researchers believe their reports likely underestimate the true prevalence of the infection in early medieval Lauchheim. Krause-Kyora notes: “Once all the soft tissues have been broken down, only blood-borne pathogens can be reliably identified in the bones. When you consider this limitation along with the degradation of DNA molecules that occurs over time, some infections likely went undetected.”

Overall poor health and climate change

The Lauchheimers were generally in poor health, with their skeletons showing signs of infection and/or malnutrition. One of the lead authors, Prof. Almut Nebel from the Institute of Molecular Biology at Kiel University, says: “At that time, Europe was experiencing rapid climate change, known as the Late Antique Little Ice Age. Climate change can lead to crop failure and eventual famine.”

Malnutrition may have increased people’s physiological stress. “In theory, famine would debilitate the malnourished population and allow pathogens to spread more easily through the community. These people were in very poor health and conditions seemed favorable for disease spread and pathogen development,” adds Nebel.

The study offers a new, temporal perspective on the burden of infectious diseases in a community living in an era characterized by high exposure to pathogens, rapid cultural change and major climate changes. In a way, these conditions are still understandable today – in times of emerging and re-emerging infectious diseases and climate change.

“This study is also a good example of the cooperation between different disciplines at the CAU. Expertise and resources from the Collaborative Research Center 1266, the ROOTS Cluster of Excellence and the Precision Medicine Cluster of Excellence have come together to learn more about the history of human diseases and draw possible lessons for us today,” says Ben Krause-Kyora.

More information:
Joanna H. Bonczarowska et al., Pathogen Genomics Study of an Early Medieval Community in Germany Shows Extensive Co-Infections, genomic biology (2022). DOI: 10.1186/s13059-022-02806-8

Provided by the Cluster of Excellence ROOTS

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