Leprosy's ancestral origins traced in latest genetic research across North and South America
In a groundbreaking study, an international team of researchers led by Dr. Maria Lopopolo from the Institut Pasteur has uncovered evidence of the bacterium Mycobacterium lepromatosis in 4,000-year-old human skeletons from Chile[1][3][5]. This discovery establishes that the causative agent of leprosy, or Hansen’s disease, has a deep, indigenous presence in the Americas, predating European contact by millennia.
The study, published in "Science", fundamentally challenges the theory that leprosy only reached America with European colonial powers or enslaved people. The genomic evidence shows that Mycobacterium lepromatosis evolved independently in the Americas for at least 12,600 years, likely emerging around 27,000 years ago[3]. This implies the pathogen was established in the continent even before the peopling of South America itself.
The study involved researchers from the Institut Pasteur, CNRS, and the University of Colorado, who analyzed nearly 800 DNA samples, including 408 current cases from Mexico, Brazil, and the USA. The discovery of the ancient genomes in Chile is particularly significant because Mycobacterium lepromatosis primarily affects internal organs such as the liver and spleen, leaving fewer traces in the skeleton, making it difficult to detect despite its apparent prevalence[4].
The bacterium Mycobacterium lepromatosis split from Mycobacterium leprae up to a million years ago. While M. leprae likely arrived in the Americas later (possibly through Old World contact), M. lepromatosis was endemic to the New World[1][2]. This finding radically revises the long-held belief that leprosy was introduced to the Americas by Europeans during colonization.
The discovery forces a reassessment of leprosy’s epidemiology. It suggests leprosy in the Americas was not simply imported from Europe but was part of a long-standing American disease ecology—undoubtedly affecting prehistoric populations[3][5]. Previous archaeological surveys failed to identify leprosy evidence in pre-contact America, reinforcing the "European import" narrative. The genomic analysis reveals those approaches likely missed M. lepromatosis due to its rarity and the subtlety of skeletal markers, hinting at a more cryptic past presence[3].
This discovery expands understanding of human migration, pathogen evolution, and disease transmission dynamics in the ancient Americas. It shows ancient indigenous peoples had endemic infectious diseases previously thought to be Old World imports[3][4]. The bacterium Mycobacterium lepromatosis was found in ancient human remains from northern Canada and southeastern Argentina, regions over 10,000 kilometers apart. In one case, a genetically unique ancestral strain was even found in a living patient in North America.
The results of the study showed that today's bacterial strains are almost identical to the old ones, indicating a long, stable presence of the pathogen in America. The researchers analyzed DNA samples from over a thousand years ago, which were genetically almost identical, suggesting rapid, continent-wide spread. This profoundly influences how scientists view the spread, evolution, and historical burden of leprosy globally[1][3][5].
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- The study's findings on the ancient presence of Mycobacterium lepromatosis in the Americas challenge the conventional wisdom about the origins of medical-conditions like leprosy, suggesting a deep-rooted indigenous presence that predates European contact.
- As scientific inquiry continues, the genomic analysis of Mycobacterium lepromatosis has potentially far-reaching implications, not only for understanding the evolution of chronic diseases but also for shedding light on the early history of human migration patterns.
