New research by an international team has revealed that there was much more diversity in the leprosy strains circulating in Medieval Europe than previously thought. This finding, based on the sequencing of 10 new ancient genomes from the leprosy-causing bacterium Mycobacterium leprae, complicates prior assumptions about the origin and spread of the disease, and also includes the oldest M. leprae genome sequenced to date, from about 400 AD in the United Kingdom.