Molecular epidemiology and transmission dynamics of leprosy among multicase families and case-contact pairs.

BACKGROUND: Human-to-human transmission of Mycobacterium leprae among household contacts of active leprosy cases is significant, and surveillance of household contacts is vital to interrupting the transmission chain for this disease. This study was conducted to identify similarities in M. leprae strains, based on genomic single nucleotide polymorphisms (SNPs), among cases and their household contacts and in multicase families in order to decipher possible associations, transmission links, various clinical conditions of index cases that enhance person-to-person transmission, and timelines for transmission patterns. METHODS: PCR for M. leprae DNA detection (amplification of the Rlep gene) and SNP subtyping of M. leprae strains was performed for 61 index cases and one of their household contacts. Additionally, we studied six families with multiple cases of leprosy, to understand timelines of infectivity and its relation to severity of the disease in the index cases. RESULTS: Index cases with lepromatous (LL) and borderline lepromatous (BL) leprosy, together with a positive bacteriological index (BI) for M. leprae, result in a higher percentage of their contacts subclinically infected with M. leprae, with odds ratios (OR) of 6.6 (95% confidence interval (CI) 1.6-27.6) for BL and LL, and 7.07 (CI 1.41-35.41) for BI-positive index cases. 75% of the case-contact pairs had a similar SNP subtype of M. leprae. The timeline of infection in multicase families revealed that contacts were infected during the BI-positive period of the index case. CONCLUSION: Using molecular methods, we determined that positivity for M. leprae DNA in contacts of index leprosy cases was attributed to clinical characteristics of leprosy in the index cases. LL and BL forms of leprosy, together with positive BI, contributed to dissemination of infection to household contacts. In conclusion, we found a relationship between SNP subtypes within index case-contact pairs. This method can help decipher the transmission patterns and identify individuals at risk of contracting leprosy.

Identification of novel open reading frames in the intergenic regions of Mycobacterium leprae genome and detection of transcript by qRT-PCR.

Mycobacterium leprae is an unculturable obligate pathogen and causative agent for debilitating human disease leprosy. Due to reductive genome evolution M leprae genome harbours large number of pseudogenes and small number of genes (∼1600 genes and ∼1300 pseudogenes). How M leprae remained a successful human parasite with small set of genes remains poorly understood and provided us the impetus to investigate the intergenic regions of M leprae genome for the presence of possible open reading frames (ORFs). In this work, we have manually scanned all the intergenic regions of M leprae genome and identified 106 potential ORFs. Among these, 12 are large ORFs: encoding hypothetical proteins (HP) of more than 100 amino acids. We have also found 67 ORFs encoding 50-100 amino acids proteins and another 27 ORFs for 30-50 amino acids peptides. We have validated the presence of transcripts for large HPs by quantitative reverse transcriptase PCR (qRT-PCR). Our results suggest that some of the M leprae large HPs are indeed expressed at low level in leprosy patients. The present results will shed light on the intergenic ORFs of M leprae and further our understanding of the pathogenesis of leprosy.