Medieval Leprosy Genomes Shed Light On Disease's History

An international team of scientists reconstructed a dozen medieval and modern leprosy genomes - suggesting a European origin for the North American leprosy strains found in armadillos and humans, and a common ancestor of all leprosy bacteria within the last 4000 years.

It is the first time scientists have reconstructed an ancient genome without a reference sequence (de novo) due to the extraordinary preservation of the medieval pathogen's DNA. This finding indicates that ancient bacterial DNA may survive in some cases much beyond the one million year boundary suggested for vertebrate DNA.

Leprosy, a devastating chronic disease caused by the bacterial pathogen Mycobacterium leprae, was prevalent in Europe until the late Middle Ages. Today, the disease is found in 91 countries worldwide with about 200,000 new infections reported annually. To retrace the history of the disease, an international team of scientists, led by Johannes Krause from Tübingen University and Stewart Cole from EPFL Lausanne, have reconstructed entire genome sequences of M. leprae bacteria from five medieval skeletons that were excavated in Denmark, Sweden and the United Kingdom as well as seven biopsy samples from modern patients.

The researchers compared the medieval European M. leprae genomes with 11 worldwide modern strains, including the seven biopsy strains, revealing that all M. leprae strains share a common ancestor that existed within the last 4000 years. This is congruent with the earliest osteological evidence for the disease in the archaeological records dated to 2000 BC from India. The genome comparisons indicate a remarkable genomic conservation of the bacteria during the past 1,000 years.