Mycobacterium leprae transmission characteristics during the declining stages of leprosy incidence: A systematic review

Abstract

Background Leprosy is an infectious disease caused by Mycobacterium leprae. As incidence begins to decline, the characteristics of new cases shifts away from those observed in highly endemic areas, revealing potentially important insights into possible ongoing sources of transmission. We aimed to investigate whether transmission is driven mainly by undiagnosed and untreated new leprosy cases in the community, or by incompletely treated or relapsing cases. Methodology/Principal findings A literature search of major electronic databases was conducted in January, 2020 with 134 articles retained out of a total 4318 records identified (PROSPERO ID: CRD42020178923). We presented quantitative data from leprosy case records with supporting evidence describing the decline in incidence across several contexts. BCG vaccination, active case finding, adherence to multidrug therapy and continued surveillance following treatment were the main strategies shared by countries who achieved a substantial reduction in incidence. From 3950 leprosy case records collected across 22 low endemic countries, 48.3% were suspected to be imported, originating from transmission outside of the country. Most cases were multibacillary (64.4%) and regularly confirmed through skin biopsy, with 122 cases of suspected relapse from previous leprosy treatment. Family history was reported in 18.7% of cases, while other suspected sources included travel to high endemic areas and direct contact with armadillos. None of the countries included in the analysis reported a distinct increase in leprosy incidence in recent years. Conclusions/Significance Together with socioeconomic improvement over time, several successful leprosy control programmes have been implemented in recent decades that led to a substantial decline in incidence. Most cases described in these contexts were multibacillary and numerous cases of suspected relapse were reported. Despite these observations, there was no indication that these cases led to a rise in new secondary cases, suggesting that they do not represent a large ongoing source of human-to-human transmission.

Mycobacterial skin infection

“…Although the incidence of leprosy has declined by 95% since the introduction of multidrug therapy (MDT) in the 1980 s, it has plateaued in the last decade [ 30 , 31 ▪▪ ]. The current stagnation in leprosy incidence has been attributed both to the large number of undetected cases, who contribute to furthering human to human transmission, and to the role of animal and environmental reservoirs [ 28 ▪▪ , 31 ▪▪ , 32 ]. Armadillo species and red squirrels were found to be wildlife reservoirs of M. leprae [ 31 ▪▪ , 33 ].…”

“…The current stagnation in leprosy incidence has been attributed both to the large number of undetected cases, who contribute to furthering human to human transmission, and to the role of animal and environmental reservoirs [ 28 ▪▪ , 31 ▪▪ , 32 ]. Armadillo species and red squirrels were found to be wildlife reservoirs of M. leprae [ 31 ▪▪ , 33 ]. Viable M. leprae has also been detected from environmental sources (water and soil) in Indonesia, India, Brazil and Bangladesh [ 34 ].…”

“…Pure neuritic leprosy without skin lesions is common in Nepal, Brazil and India (4–18% of Indian leprosy cases). In such cases, mononeuritis is the most common presentation [ 36 ], especially in older patients, suggesting the effectiveness of national control measures against child leprosy [ 31 ▪▪ ].…”

Lepromatous leprosy with a suspected 30-year incubation period: A case report of a practically eradicated area

“…Leprosy is a neglected tropical disease that is considered rare in most regions despite having relatively high incidence in some countries. 1 It is caused by infections with Mycobacterium leprae and Mycobacterium lepromatosis . Transmission occurs via droplets during close and frequent contact with untreated cases.…”

“…Transmission occurs via droplets during close and frequent contact with untreated cases. 1 Both M. leprae and M. lepromatosis are slow-growing bacteria with incubation periods varying from 5 to 10 years, depending on clinical subtypes. 2 The clinical presentations of leprosy include skin rash, peripheral neuropathy, and organ deformities.…”