Ancient-DNA reveals an Asian type of Mycobacterium leprae in medieval Scandinavia

Leprosy is a chronic infection of the skin and peripheral nerves caused by the pathogen Mycobacterium leprae. Its impact on human populations and societies of the past as well as its phylogeographic patterns around the world - at least in modern times - has been well documented. This slow growing bacterium has been shown to exist in distinct 'SNP types' that occur in relatively defined parts of the globe. The routes that the disease followed in the past are, however, still uncertain. This study of ancient-DNA typing of archaeological human remains from Sweden dated to early Medieval times provides genetic evidence that a transmission of M. leprae 'SNP subtype' 2G - found mainly in Asia - took or had already taken place at that time from the Middle East to Scandinavia. This finding is unique in the history of leprosy in Europe. All human specimens from this continent - both modern and ancient - that have been tested to date showed that the one responsible for the infection strains of M. leprae belong to 'SNP type' 3, whereas our results show that there were some European populations that were hosts to bacteria representing 'SNP type' 2 of the species as well. (C) 2012 Elsevier Ltd. All rights reserved.