Transmission features of Mycobacterium leprae throughout the decline of leprosy incidence

Background: Mycobacterium leprae causes leprosy, an infectious disease. As the incidence of the disease declines, the characteristics of new cases begin to diverge from those seen in highly endemic locations, offering potentially valuable insights into ongoing transmission sources. We wanted to see if undiagnosed and untreated new leprosy cases in the community drive transmission more than incompletely treated or relapsing cases. Principle findings/methodology: In January of 2020, a literature search of major electronic databases yielded 134 articles out of 4318 total entries found (PROSPERO ID: CRD42020178923). We presented quantitative data from leprosy case records, along with supporting evidence, to describe the drop in incidence in a variety of settings. The major measures used by countries that achieved a significant reduction in incidence included BCG vaccination, active case detection, adherence to combination therapy, and continuous surveillance after treatment. In a study of 3950 leprosy case data from 22 low-endemic nations, 48.3% were thought to be imported, beginning from transmission outside the country. With 122 cases of suspected relapse from earlier leprosy treatment, the majority of cases (64.4%) were multibacillary and frequently verified with skin biopsy.