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Epidemic: How leprosy changed the genetic makeup of all Europeans


Old genomes offer new insights into inflammatory diseases

In medieval Europe, leprosy was widespread until the 16th century and caused veritable epidemics. In the course of the 16th century, the contagious infectious disease almost completely disappeared from Europe. At that time, there were no antibiotics that are used today to treat this disease. In the world's first study of this kind, an international research group examined bones of lepers from the 12th and 13th centuries. The findings from this work should also enable conclusions to be drawn about today's inflammatory diseases.

Apparently, an adaptation in the genome of Europeans meant that the disease did not spread any further. According to the scientists led by Professor Ben Krause-Kyora from the Institute for Clinical Molecular Biology (IKMB) at Christian-Albrechts-Universit├Ąt zu Kiel (CAU), a certain gene made people more susceptible to leprosy. By consistently isolating the sick from the rest of the population, this gene was passed on less and less and eventually disappeared, and with it the leprosy. The research results were recently published in the renowned journal "Nature Communications".

Leprosy today

The medieval illness is far from over. According to the IKMB, over 200,000 people worldwide still contract this infectious disease every year. Risk areas include Brazil, India and Indonesia. Today, however, leprosy is curable with antibiotics. The World Health Organization reports that leprosy with few pathogens (paucibacillary leprosy) can be cured by treatment with certain antibiotics for six months. If there are many pathogens (multibacillary leprosy), antibiotic therapy over a period of two years is required.

Genome change through isolation

The researchers report that those affected in the European Middle Ages were isolated in larger outbreaks in care facilities and buried in separate cemeteries. Due to the isolation and the fact that lepers could not have offspring, the sick did not pass on a certain risk factor. "The adaptation of humans to this bacterium over centuries could have caused the disease to slowly disappear," study leader Krause-Kyora reports in a press release on the study results. This suggests that leprosy and other past epidemics have had a lasting impact on the composition of our genome today.

Danish bones

For their analyzes, the scientists used the bones of 85 particularly serious leprosy cases from the 12th century, which originate from Odense in Denmark. Samples from 223 medieval Danish and north German skeletons that showed no traces of leprosy served as a control group. These analyzes showed that a certain gene variant (HLA-DRB1) is associated with an increased susceptibility to leprosy.

Conclusions about today's medicine

According to the scientists, the HLA gene variant still causes an increased incidence of inflammatory diseases such as sarcoidosis, chronic inflammatory bowel disease, ulcerative colitis, multiple sclerosis or type 1 diabetes. Antigens usually recognize bacteria and trigger a targeted immune response in the body. In the case of the identified HLA variant, this task is unsuccessful, particularly with the leprosy bacteria. This may result in a less successful immune response.

Interactions between pathogens and humans

"Research into historical causes of illness is crucial to understanding the interactions between pathogens and humans, and the resulting changes in our genome over time," summarizes Krause-Kyora. The team is already planning new research into other diseases of the Middle Ages in various population groups to track how the genetic makeup of Europeans has changed. (vb)

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