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**A Groundbreaking Discovery: Rewriting the History of Leprosy in the Americas**
For centuries, leprosy—also known as Hansen’s disease—has been one of the world’s most misunderstood and stigmatized infectious diseases. Historically, it has been associated with myths, social ostracism, and a deep sense of fear. In the Americas, conventional wisdom long held that leprosy arrived with the first European explorers and settlers, who brought with them a host of new diseases that devastated Indigenous populations. However, a new scientific breakthrough led by researchers from the Institut Pasteur in Paris, in collaboration with the University of Colorado and other international partners, is dramatically altering our understanding of when and how this disease first appeared in the western hemisphere.
**Challenging the Long-Held Narrative**
Until recently, the scientific consensus was straightforward: leprosy in the Americas was believed to be caused solely by the bacterium *Mycobacterium leprae*, and it was introduced by Europeans after 1492. This view fit neatly into the broader narrative of Old World diseases being brought to the New World during the so-called Age of Exploration, causing catastrophic epidemics among Indigenous peoples who lacked immunity.
This new research, however, has upended that narrative. The team at the Institut Pasteur, working alongside the French National Center for Scientific Research and the University of Colorado, has discovered compelling evidence that a second species of leprosy-causing bacteria was present in the Americas long before European contact. This species, *Mycobacterium lepromatosis*, was found to have infected humans in the Americas as far back as 1,000 years prior to the arrival of Columbus and other explorers. In essence, leprosy was not a foreign invader brought by settlers, but rather a disease already established among Indigenous populations.
**The Significance of the Discovery**
Dr. Maria Lopopolo, the first author of the study and a researcher at the Laboratory of Microbial Paleogenomics at the Institut Pasteur, emphasized the transformative nature of this finding. “This discovery transforms our understanding of the history of leprosy in America. It shows that a form of the disease was already endemic among Indigenous populations well before the Europeans arrived,” she stated in the official release.
This revelation has enormous implications for our understanding of disease ecology, human migration, and the interaction between humans and pathogens in the pre-Columbian Americas. It also challenges some of the assumptions about the impact of European colonization on Indigenous health, suggesting that at least some diseases predated European contact and were part of the epidemiological landscape long before the so-called “Columbian Exchange.”
**Tracing the Origins of Leprosy in the Americas**
The new study was prompted by several intriguing discoveries over the past two decades. In 2008, *Mycobacterium lepromatosis* was identified in a patient from Mexico. Later, in 2016, the same species was found in red squirrels in the British Isles—a surprising twist that raised questions about the pathogen’s distribution and history.
To get to the bottom of this mystery, the researchers utilized advanced genetic sequencing techniques to reconstruct the genomes of *Mycobacterium lepromatosis* from ancient human remains found in Argentina and Canada. The goal was to determine how long this bacterium had been present in the Americas and how it might have spread.
Their genetic analysis revealed that the two ancient strains—from geographically distant regions in North and South America—were closely related on the family tree of *Mycobacterium* species. This genetic closeness indicates that *M. lepromatosis* had spread rapidly and widely across the continent, long before the arrival of Europeans. The results provide compelling evidence that the disease was not imported wholesale from Europe; rather, it had already taken root and diversified among Indigenous populations.
**A Collaborative and Interdisciplinary Effort**
This study was notable not only for its scientific rigor but also for its collaborative approach. The researchers worked closely with Indigenous communities, archaeologists, and various international institutions. Over 800 DNA samples were analyzed, drawn from ancient human remains and recent medical cases where leprosy was suspected. This comprehensive dataset allowed the team to track the genetic diversity and geographical spread of leprosy-causing bacteria over a millennium.