A groundbreaking new study has upended longstanding assumptions about the history of leprosy in the Americas, revealing that one species of the leprosy-causing bacterium was present in human populations long before the arrival of Europeans. For centuries, it was widely believed that leprosy was introduced to the Americas solely through European colonization, but recent findings demonstrate that the disease’s roots in the Western Hemisphere stretch back well before recorded European contact. Central to this discovery is Mycobacterium lepromatosis, a relatively recently identified species that alongside Mycobacterium leprae, is responsible for causing leprosy.
Leprosy, also known as Hansen’s disease, is a chronic infectious condition affecting primarily the skin and peripheral nerves, and has been plaguing humanity for millennia. Traditionally, research and historical records have focused heavily on M. leprae, the species most commonly associated with the disease, especially in Europe and Asia. However, M. lepromatosis, only identified in 2008, has emerged as a crucial piece of the puzzle, particularly due to its predominance in cases reported in the Americas. Unlike M. leprae, whose introduction aligns closely with European colonization patterns, the evolutionary and historical trajectory of M. lepromatosis remained largely enigmatic until now.
The investigative team, led by Maria Lopopolo, undertook a comprehensive genomic analysis aimed at elucidating the presence, diversity, and historical timeline of M. lepromatosis in the Americas. Utilizing both contemporary DNA sequences and ancient genetic material extracted from archaeological human remains dating to periods before European arrival, the researchers mapped the distribution of M. lepromatosis across the continent. This dual approach allowed them to peer into the past, bridging modern molecular techniques with paleomicrobiology to chart the evolutionary history of this neglected pathogen.
Prior to this study, genomic data of M. lepromatosis were scarce and geographically limited. Available sequences mainly originated from a handful of Mexican patients and red squirrels from parts of Great Britain and Ireland, which constrained the ability to understand the bacterium’s variability and distribution. Such limitations hindered deeper insights into how and when the bacterium had spread into the Americas or interacted with human populations. By expanding the dataset with ancient DNA samples, the new research delivers critical evidence that challenges previous epidemiological models.
The analysis revealed that M. lepromatosis was endemic in human groups throughout the Americas well before European colonization. Specifically, ancient DNA screenings from pre-contact ancestral remains identified M. lepromatosis infections in diverse geographical regions spanning from northern to southern parts of the continent. This widespread presence suggests that M. lepromatosis had established itself over centuries, if not millennia, within Native American communities. Consequently, its epidemiological history is far more complex than a mere post-contact introduction.
Importantly, the study emphasizes that these findings do not dispute the well-documented introduction of M. leprae by Europeans and Africans during colonial times, which undoubtedly contributed to the modern epidemiology of leprosy in the Americas. Instead, the nuanced results indicate that the two species have distinctly different histories on the continent. While M. leprae’s dissemination aligns with documented migration and trade routes, M. lepromatosis appears to have had an independent, pre-contact trajectory, underscoring a much earlier chapter in the history of infectious diseases within indigenous populations.
This revelation carries profound implications for our understanding of human-pathogen coevolution. The presence of M. lepromatosis in pre-Columbian America invites a reconsideration of how infectious diseases developed and spread in isolation from Old World influences. It underscores the need to incorporate indigenous epidemiological histories that have been historically overlooked, both in scientific scholarship and in public health frameworks targeting leprosy.
The technical methodology employed was meticulous, incorporating high-throughput sequencing technologies adapted for degraded ancient samples. This enabled the recovery of pathogen genetic material from skeletal remains dated prior to the 15th century, a cutting-edge achievement that opens new vistas in paleopathology. Alongside this, comparative genomics analyses helped define the phylogenetic positioning of the recovered M. lepromatosis strains relative to contemporary isolates, revealing evolutionary divergences that predate European contact.
Moreover, the study sheds light on the zoonotic potential of M. lepromatosis, a dimension underscored by the presence of genetically similar strains in non-human hosts such as red squirrels in Europe. These cross-species associations provoke intriguing questions about the ecological niches and transmission dynamics of the bacterium, particularly whether animal reservoirs contributed to its persistence or geographical spread before human colonization events.
From a clinical perspective, distinguishing between M. leprae and M. lepromatosis carries significant weight. Both species cause different forms and severities of leprosy, with variations in disease progression and response to treatment. Historically, the lumping of these pathogens under a single disease umbrella may have obscured critical insights needed for tailored therapeutic strategies, especially in endemic regions of the Americas where M. lepromatosis predominates.
The study’s interdisciplinary approach also exemplifies the power of integrating genomics, archaeology, infectious disease biology, and anthropology to solve long-standing scientific mysteries. It bridges temporal gaps between ancient historical records and cutting-edge molecular biology, enriching our narratives about pathogen evolution and human history. This holistic perspective is essential for comprehensively tackling the legacies of infectious diseases.
In conclusion, this research fundamentally revises prevailing narratives on the origins and diversity of leprosy in the Americas. It reveals that Mycobacterium lepromatosis, a bacterium only recently identified, has been silently infecting indigenous populations across the continent for centuries prior to European colonization. These insights challenge simplified stories of post-contact disease introduction and open new pathways for understanding the complexity of human-pathogen interactions in the Americas. As the scientific community reassesses leprosy’s evolutionary history, these findings could stimulate renewed attention towards neglected tropical diseases and their deep historical roots.
The significance of uncovering pre-contact leprosy infections extends beyond academic curiosity—it holds profound implications for modern public health policies, diagnosis, and surveillance in endemic areas. By acknowledging the ancient and endemic nature of M. lepromatosis infections, health authorities can better anticipate patterns of disease persistence and transmission. Furthermore, the revelation may inspire new research exploring other pathogens that might share similarly underappreciated historical trajectories within indigenous populations.
This study exemplifies how advances in paleogenomics can revolutionize our understanding of diseases once thought well-characterized. It challenges us to reexamine the complex webs of interaction between humans and their microbial companions throughout history, emphasizing that even ancient DNA holds lessons with contemporary relevance. As research continues, the story of leprosy in the Americas promises to inform broader discussions on migration, colonization, and the invisible biological legacies carried forward across generations.
Subject of Research: Leprosy in the Americas, Mycobacterium lepromatosis, paleogenomics, infectious disease history
Article Title: Pre-European contact leprosy in the Americas and its current persistence
News Publication Date: 29-May-2025
Web References: http://dx.doi.org/10.1126/science.adu7144
Keywords: leprosy, Mycobacterium lepromatosis, Mycobacterium leprae, ancient DNA, paleogenomics, infectious diseases, pre-Columbian America, Hansen’s disease, pathogen evolution, indigenous populations
