Researchers have analysed the genome sequences of Mycobacterium leprae samples from the teeth and bones of mediaeval skeletons.
M. leprae is the bacillus that causes leprosy, which was endemic in Europe until mediaeval times; whilst cases have dropped world-wide, it persists in regions outside Europe, especially South-East Asia. M.leprae DNA was isolated from a total of five 10th – 14th century skeletons from mediaeval leper colonies in the UK, Sweden and Denmark, where it comprised a surprisingly high proportion of the total DNA present.
Genome sequences were obtained and compared with a selection of modern strains; this revealed that three of the ancient European genomes showed very high similarity with a modern strain from the Middle East, and two with modern strains found in the Americas.
Understanding the history of how infectious diseases and human populations have evolved over time is important for predicting future risks and developing effective strategies for prevention and treatment of new and more virulent pathogens. Genome sequencing of ancient pathogens such as Yersinia pestis that causes plague (see previous news) is an area of increasing scientific activity.
In this instance, the results support previous suggestions that the Crusades spread leprosy to the Middle East where is persists today, whilst virtually dying out in Europe by the sixteenth century. The high degree of sequence similarity between the ancient European and modern Middle-Eastern leprosy genomes suggests that the Caucasian European populations gradually developed immunity to the disease, rather than the M.leprae losing any virulence. The link between ancient European and modern American strains also suggests that the disease originated from Europe.
The unusually high level of mycobacterial DNA found in the skeletal samples is attributed to the lipid-rich cell membranes, presumed to offer much greater protection than normal bacterial membranes; the researchers propose that it is therefore theoretically possible that M. leprae samples from skeletons over a million years old could also be sequenced.