Evolutionary history of Mycobacterium leprae in the Pacific Islands

Area of Science:

• Genomics
• Epidemiology
• Anthropology

Background:

• Leprosy (Hansen's disease) is an ancient infectious disease caused primarily by Mycobacterium leprae.
• The historical introduction of M. leprae to the Pacific Islands is debated, with theories suggesting colonial-era or older origins.
• Understanding the genomic variation and phylogeography of M. leprae is crucial for public health and historical insights.

Purpose of the Study:

• To investigate the origins and introduction patterns of Mycobacterium leprae in the Pacific Islands.
• To analyze the genomic variation and phylogeography of M. leprae strains from the Pacific region.
• To provide evidence for the historical timeline of leprosy transmission in the Pacific.

Main Methods:

• DNA extraction from 39 formalin-fixed paraffin-embedded biopsy blocks (1992-2016).
• Whole-genome enrichment and next-generation sequencing to generate nine M. leprae genomes (1998-2015).
• Phylogenetic and phylogeographical analyses, including evolutionary dating.

Main Results:

• Nine M. leprae genomes were successfully sequenced, with coverage ranging from 4-63×.
• Phylogenetic analysis placed these Pacific strains within basal lineages (branches 0 and 5) of the M. leprae phylogeny.
• Phylogeographical patterns and evolutionary dating support a pre-modern introduction of M. leprae to the Pacific Islands.

Conclusions:

• The genomic data suggest that leprosy was established in the Pacific Islands before the 19th century colonial period.
• This study refutes the sole reliance on colonial history for understanding leprosy introduction in the region.
• The findings contribute to the understanding of pathogen exchange and the deep history of infectious diseases in the Pacific.