From an evolutionary perspective, one highly interesting group of pathogens is the Mycobacterium genus. It includes bacteria known to cause serious disease in mammals, including tuberculosis (M. tuberculosis), leprosy (M. leprae), or tuberculosis in cattle (M. bovis).
In a multinational cooperation, we successfully sequenced the complete M. leprae genomes of six individuals from the medieval era. DNA retrieved from the teeth of one leper was so well-preserved that full de novo assembly of the ancient M. leprae genome was possible through shotgun sequencing alone. Phylogenetic comparison of the obtained sequence against four publicly available M. leprae genomes as well as nine modern M. leprae genomes newly sequenced for this study revealed that the disease probably emerged in humans about 4,000 years ago. This data corroborates the assumption that sedentism and the increased population density that followed early urbanization facilitated the emergence and spread of many infectious diseases.
It is still unclear why leprosy disappeared from Europe as a major health risk during the 16th century. The absence of genetic variations in the M. leprae genome, which could have created a shift in virulence during the last 1,000 years that made leprosy less of a health threat, suggests that the decrease in disease prevalence in Europe is linked to human host genetics and environmental factors, e.g. co-infections with tuberculosis, immunization through infections with bovine tuberculosis or societal/environmental changes.
In further studies, we aim to unravel the interplay between the infectious diseases caused by the three Mycobacteria species in northern Europe between the 11th and 16th centuries.
Involved PhD students: Marion Bonazzi and Marcel Nutsua.
For more details see also the corresponding Junior Research Group.
The project is supported by the Graduate School Human Development in Landscapes.