A groundbreaking study led by scientists from the Institut Pasteur in Paris, in collaboration with the French National Centre for Scientific Research and the University of Colorado, has fundamentally altered our understanding of the history of leprosy, also known as Hansen's disease, in the Americas. For many years, it was widely believed that leprosy in the New World was caused solely by the bacterium Mycobacterium leprae and that it was introduced to the Americas by European explorers and settlers during the colonial period. However, new genetic evidence has revealed the presence of a second species of bacteria, Mycobacterium lepromatosis, that had been infecting Indigenous populations in the Americas for over a millennium prior to European contact.
This discovery challenges the long-held assumption that leprosy was a disease brought exclusively by Europeans and suggests instead that the disease was already endemic among Indigenous peoples long before the arrival of European colonizers. Dr. Maria Lopopolo, the lead author of the study and a researcher at the Laboratory of Microbial Paleogenomics at the Institut Pasteur, emphasized the significance of this finding, stating that it “transforms our understanding of the history of leprosy in America.” Essentially, the presence of Mycobacterium lepromatosis rewrites the narrative about the origins and spread of leprosy in the Western Hemisphere.
The study began after the bacterium Mycobacterium lepromatosis was first identified in a Mexican patient in 2008 and later found in red squirrels in the British Isles in 2016, raising questions about its geographic distribution and history. Using advanced genetic sequencing techniques, the researchers reconstructed the genomes of Mycobacterium lepromatosis from ancient human remains excavated from sites in Argentina and Canada. These genomic analyses showed that the strains of the bacterium found in these widely separated locations were genetically very similar, indicating that the bacterium had spread rapidly throughout both North and South America over a long period of time.
By examining over 800 DNA samples taken from ancient human remains as well as recent medical cases exhibiting signs of leprosy, the researchers were able to map the historical presence and diversity of this neglected pathogen. This extensive sampling was conducted in collaboration with Indigenous communities, archaeologists, and international scientific institutions, underscoring the multidisciplinary and cross-cultural nature of the research. Nicolás Rascovan, the lead author of the study at the Institut Pasteur, highlighted the broader implications of their findings, noting that the research not only reshapes history but also opens new avenues for understanding the disease’s transmission. He suggested that there may be unknown animal reservoirs of the bacterium that could play a role in its persistence and spread.
Leprosy is a chronic infectious disease that primarily affects the skin, peripheral nerves, and eyes. The Centers for Disease Control and Prevention (CDC) explains that while it is a potentially disabling disease if left untreated, it can be effectively managed with a regimen of antibiotics. Worldwide, about 250,000 new cases are reported annually, with approximately 225 new cases occurring each year in the United States. The revelation that leprosy has a deeper and more complex history in the Americas than previously thought could have significant implications for public health, epidemiology, and our understanding of infectious diseases in Indigenous populations.
The discovery of Mycobacterium lepromatosis in ancient remains predating European colonization not only changes the timeline of leprosy’s arrival in the Americas but also raises important questions about how the disease evolved and spread across continents. It suggests that Indigenous peoples were affected by this disease for centuries, which may have influenced social and health dynamics in pre-Columbian societies. Furthermore, the rapid spread of the bacterium across vast geographic regions, evidenced by genetic similarities in samples from Argentina and Canada, points to complex patterns of human migration and contact that facilitated the dissemination of the disease.
This research also exemplifies the power of modern genetic and paleogenomic methods to unlock hidden chapters of human history. By extracting and analyzing ancient DNA, scientists can reconstruct the evolutionary history of pathogens and better understand their interactions with human hosts over time. Such studies provide crucial insights into the origins and trajectories of infectious diseases, which is essential for developing strategies to control them today.
While the study fundamentally revises the historical narrative of leprosy in the Americas, it also underscores the importance of continued surveillance and research into neglected diseases that persist in various parts of the world. The identification of a second causative bacter