Detection of Mycobacterium leprae DNA in soil; Multiple needles in the haystack?

BackgroundLeprosy is an infectious disease caused by Mycobacterium leprae and Mycobacterium lepromatosis affecting the skin and nerves. Despite decades of availability of adequate treatment, transmission is unabated and routes of transmission are not completely understood. Notwithstanding the general assumption that untreated M. leprae infected humans represent the major source of transmission, scarce reports indicate that environmental specimens could play a role as a reservoir as well.\n\nMethodologyIn order to identify patterns of bacterial transmission, this study investigated whether M. leprae DNA is present in soil of regions where leprosy is endemic or areas with possible animal reservoirs (armadillos and red squirrels). Soil samples were collected in Bangladesh, Suriname and the British Isles. The presence of M. leprae DNA was determined by RLEP PCR and M. leprae SNP types were further identified by Sanger sequencing of loci 1-3.\n\nResultsM. leprae DNA was identified in soil samples from environments inhabited by leprosy patients (Bangladesh), armadillos (Suriname) and the lepromatous Eurasian red squirrels (British Isles). In Bangladesh SNP type 1 was detected, Suriname soil contained SNP type 1 or 2, whilst SNP typing was not feasible for the British samples.\n\nConclusionsIt is conceivable that, besides humans and animals, environmental reservoirs may play a role in transmission. Frequent, intense contact with multibacillary leprosy patients poses the highest risk of transmission, and even though the risk of environmental contamination is low, it may offer a possible explanation for the occurrence of leprosy in individuals in areas without any reported human leprosy.