Survival of Mycobacterium leprae and association with Acanthamoeba from environmental samples in the inhabitant areas of active leprosy cases: A cross sectional study from endemic pockets of Purulia, West Bengal

Mycobacterium leprae being an obligate intracellular parasite cannot be cultured in any artificial culture media but it has been shown to reside in wild armadillos in North America. Many studies suggested that M. leprae could be found in the environment and may have a role in continuing transmission of the disease. The exact role of the environment in the transmission dynamics is still speculative. The present study was undertaken to find out the presence of viable M. leprae around patients' environment like soil and water and association of free living pathogenic protozoa, Acanthamoeba which might play an important role in transmission of the disease.Seven hundred soil and 400 water samples were collected from the surroundings of the houses of leprosy patients from endemic villages. Two hundred soil and 80 water samples were also collected from the surroundings of normal inhabitants from non-endemic villages as controls. These samples were screened for the presence of M. leprae and Acanthamoeba using DNA PCR. RNA was extracted from the PCR positive samples and Reverse Transcriptase - PCR targeting 16S rRNA gene region was performed for detection of viable M. leprae.We observed high PCR positivity in soil samples (218 out of 700; 31%) and water samples (73 out of 400; 18%). These samples when further screened for viability, it was observed that 106 soil samples (15% of total) and 34 water samples (8% of total) showed presence of 16S rRNA. We observed 18.3% of soil and 20.5% of water samples were PCR positive for Acanthamoeba. Soil samples from the control area, where no active leprosy case resided in the last 5 years, showed PCR positivity in 4 samples (2%) for M. leprae DNA in only soil samples with all water samples being negative. RT-PCR for all PCR positive soil samples was negative. Of the 106 soil samples positive for M. leprae RT-PCR, 30 samples were also positive for Acanthamoeba whereas out of 112 M. leprae RT-PCR negative but PCR positive samples only 10 samples were Acanthamoeba positive showing association of viability with presence of Acanthamoeba (p = .0021). Similarly, for water samples also, association of M. leprae viability with presence of Acanthamoeba was seen (p = .0009).This study suggests that the surrounding environment (soil and water) of leprosy patients contain viable M. leprae and the viability has association with Acanthamoeba which may provide a protective niche for M. leprae. This could play an important role in the focal transmission of the disease.