Leprosy's Ancient American Roots Unearthed, Challenging Colonial Narrative

For centuries, the prevailing belief was that European colonizers introduced leprosy to the Americas. However, groundbreaking research reveals a startling truth: leprosy, caused by the bacterium Mycobacterium lepromatosis, was already present in the Americas over 1,000 years before European contact, rewriting the history of this stigmatized disease and raising new questions about its origins and spread.

Rewriting History with Ancient DNA

A major international study, published in Science, was co-led by scientists at Colorado State University and the Institut Pasteur in France, in collaboration with Indigenous communities and over 40 scientists from institutions across the Americas and Europe. The team analyzed DNA from nearly 800 samples, including ancient skeletal remains and modern clinical samples from Mexico, the U.S., Brazil, Paraguay, and French Guiana. This extensive screening revealed the presence of M. lepromatosis in ancient human remains from Canada and Argentina, dating back over 1,000 years.

"This discovery transforms our understanding of the history of leprosy in America," said Dr. Maria Lopopolo of the Institut Pasteur, the study's first author. "It shows that a form of the disease was already endemic among Indigenous populations well before the Europeans arrived."

A Rapid Continental Spread

The research indicates that the M. lepromatosis strains found in Canada and Argentina, despite being separated by over 10,000 kilometers, were genetically similar and within a relatively narrow time frame. This suggests a rapid, continent-wide spread of the pathogen in just a few centuries. The study leaves open the question of whether this dispersal was human-mediated, through trade and contact networks, or animal-driven.

"Our findings significantly alter the historical narrative of leprosy in the Americas," said Nicolás Rascovan, a senior author from the Institut Pasteur.

The Mystery of Mycobacterium Lepromatosis

While Mycobacterium leprae is the most common species of leprosy-causing bacteria, M. lepromatosis is a lesser-known species that was first identified in 2008 in a patient from Mexico. In 2016, it was unexpectedly found in red squirrels in the British Isles, marking the first confirmed animal reservoir of the pathogen. Genetic studies now suggest that this strain likely originated in the Americas and could have been transported to Europe during the 19th century by human or trade activity.

The discovery of M. lepromatosis has been challenging for researchers, as the bacteria is difficult to study in the lab. Unlike M. leprae, which causes distinctive bone lesions, M. lepromatosis damages blood vessels and internal organs, making it harder to detect in ancient skeletal remains.

Ethical Considerations and Indigenous Collaboration

The researchers emphasized the importance of ethical considerations in their work, particularly when dealing with ancestral remains. Indigenous communities were involved in decision-making, and DNA data were shared following protocols designed to respect their cultural expectations. Materials were also returned to communities when requested.

Unanswered Questions and Future Research

The origins of M. lepromatosis remain uncertain. Genetic information shows that it diverged from M. leprae between 700,000 and 1 million years ago. Whether the bacterium arrived in the Americas with early human migrations across the Bering Land Bridge or evolved in native animal hosts before spreading to humans is still unknown.

The study also revealed a deeply divergent variant of M. lepromatosis that still infects people in the United States. This lineage differs significantly from all other known strains and is estimated to have separated from the rest more than 9,000 years ago.

Further research is needed to understand the full extent of M. lepromatosis's presence in the Americas, its transmission pathways, and its relationship to other leprosy strains worldwide. Cataloging leprosy's past will help scientists better understand its future.

Implications for Understanding Infectious Diseases

This groundbreaking study has significant implications for understanding how infectious diseases spread, persist, and evolve in human and animal populations over time. It highlights the importance of using ancient DNA to rewrite medical history and deepen our understanding of contemporary infectious diseases. The discovery also raises the possibility that this pathogen may have been introduced in various geographic regions and highlights the necessity of continued surveillance, particularly in view of antimicrobial resistance as a growing global health challenge.

The findings challenge long-held assumptions about the introduction of leprosy to the Americas and underscore the complex interplay between humans, animals, and pathogens in shaping the history of disease.