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

Epidemiological scenario of leprosy in marginalized communities of India: Focus on scheduled tribes

The Scheduled Tribes (STs) are designated among the most disadvantaged social groups in India. Until the year 2005 (pre-elimination era of leprosy in India), several leprosy-specific control field programmes were implemented, which have been discontinued subsequently. Since then, leprosy diagnosis and treatment have been integrated with General Health Services. Thereafter, specialized expertise for the early diagnosis of leprosy has been gradually diminishing, especially at the peripheral clinics in remote areas. Hence, leprosy cases usually remain undetected for a long time and persist as endemic reservoirs. The tribal population of India accounts for just 8.6 per cent of the overall population. However, 18.5 per cent of the new leprosy cases were detected within the tribal community in the year 2020, indicating a disproportionately high burden of leprosy among the tribal population. Recent data suggest that these health disparities can be mainly related to the increased marginalization of STs as compared to other communities. This shows the need to further explore the current situation of leprosy in STs so that suitable interventions can address the contributing factors, leading to health inequalities in disadvantaged socio-economic groups. Therefore, this review aims to present the current distribution of leprosy in marginalized communities with a special emphasis on STs. Further, this review discusses how resources might be mobilized for such communities to find and treat undetected leprosy patients in STs to enable effective control of leprosy through early detection and timely treatment.

Molecular epidemiology of leprosy: An update

Molecular epidemiology investigations are notoriously challenging in the leprosy field mainly because the inherent characteristics of the disease as well as its yet uncultivated causative agents, Mycobacterium leprae and M. lepromatosis. Despite significant developments in understanding the biology of leprosy bacilli through genomic approaches, the exact mechanisms of transmission is still unclear and the factors underlying pathological variation of the disease in different patients remain as major gaps in our knowledge about leprosy. Despite these difficulties, the last two decades have seen the development of genotyping procedures based on PCR-sequencing of target loci as well as by the genome-wide analysis of an increasing number of geographically diverse isolates of leprosy bacilli. This has provided a foundation for molecular epidemiology studies that are bringing a better understanding of strain evolution associated with ancient human migrations, and phylogeographical insights about the spread of disease globally. This review discusses the advantages and drawbacks of the main tools available for molecular epidemiological investigations of leprosy and summarizes various methods ranging from PCR-based genotyping to genome-typing techniques. We also describe their main applications in analyzing the short-range and long-range transmission of the disease. Finally, we summarise the current gaps and challenges that remain in the field of molecular epidemiology of leprosy.