People thought that leprosy, also known as Hansen’s disease, came to the Americas with European colonizers hundreds of years ago. But a new study that is changing the way we think about this has come out. Researchers looking at 4,000-year-old skeletons from Chile have found genetic proof of Mycobacterium lepromatosis, a rare and severe form of leprosy. This suggests that the disease existed in the Americas long before Europeans came into contact with them. This new information changes what we thought we knew about this old disease and makes us ask important questions about how it spread, why it lasted so long, and if animals were involved in its spread.
A Stunning Preservation of Ancient Pathogen DNA
The study, which was published in Nature Ecology & Evolution, looked at the skeletons of two adult males that were dug up at the archaeological sites of El Cerrito and La Herradura in northern Chile. Researchers were shocked by how well the DNA from M. lepromatosis was preserved; it was even better than many modern samples. Lesley Sitter, who works as a computational biologist at the Max Planck Institute for Evolutionary Anthropology, commented, “The DNA was in great shape, which is rare for specimens of that age.”
The scholars managed to reconstruct nearly entire bacterial genomes employing highly advanced genomic techniques. They identified 94 distinctive mutations absent in contemporary strains. This indicates that the pathogen evolved over millennia in the Americas, completely independent of modern cases.
Two Leprosy Pathogens, Two Separate Evolutionary Paths
The first sign of Mycobacterium leprae infection can be traced back 5,000 years in Eurasia. This region holds rich historical evidence of leprosy. Recent findings from Chile, however, supports an earlier theory that M. lepromatosis, which was discovered in 2008, had been circulating in the Americas much before it was supposed to. Current genetic information indicates that the two pathogens diverged approximately 26,800 years ago, with the American branch splitting around 12,600 years ago, which is aligned with the timeline of early human migrations into South America.
This supports earlier findings that refute the widely accepted claim that leprosy was bought into South America by European settlers. Biological anthropologist Darío Ramirez states that “We were initially skeptical because leprosy is considered a colonial-era disease, but the DNA left no doubt” while discussing the study.
Did Armadillos or Other Animals Spread the Disease?
The origins of M. lepromatosis in the Americas remains particularly enigmatic. M. leprae is known to have an ecological niche within armadillos, while no animal reservoir for M. lepromatosis has been confirmed to exist. The recent discovery of the pathogen in red squirrels from England and Ireland does, however, raise some prospects of zoonotic transmission.
M. lepromatosis’s putative diphasic life cycle entails non-flagellated replicative stages in a vertebrate host, paving the way for the pathogen’s evolution and spread via an undocumented animal vector during prehistoric times, which in turn raises questions surrounding its existence in bygone eras and paleogeographies. “That’s a real possibility, but ultimately wildlife and environmental reservoirs need to be examined more closely,” Bos added, hypothesizing what could lie beyond empirical findings.
A Disease of the Forgotten: The Social Stigma of Leprosy
Leprosy has always been accompanied by stigma and social exclusion. Abandonment from society is evidenced by skeletal remains which not only show deformed bones but also display nasal collapse, finger erosion, and limb twisting. Chilean skeletal remains are characterized by some of these features such as deep-set nasal bones and hand bones indicative of leprosy. However, researchers warn that these features can result from other diseases too.
The understanding that M. lepromatosis existed in pre-Columbian societies adds to the shadowy legacy of the disease. Bos states, “This wasn’t just a European import, it was already shaping lives in the Americas.”
Why This Changes Our Understanding of Ancient Diseases
The results show how little we still know about pathogens from the past. Leprosy was just one of many diseases that killed a lot of people before Europeans came. Most of these diseases were forgotten after the terrible epidemics that followed European contact. “Ancient DNA lets us find lost parts of human suffering,” Bos said.
The study also shows how important it is to look at human, animal, and environmental factors together in a “One Health” way to figure out how diseases like leprosy keep coming back. It could be very important for modern public health to learn more about these old pathogens because climate change and deforestation could make new reservoirs more accessible.
What’s Next? Hunting for More Ancient Clues
The discovery in Chile is very important, but there are still many questions. Did M. lepromatosis start in the Americas, or did it come with the first people who moved there? Are there still animal carriers that haven’t been found? Researchers want to look at more skeletal remains from all over the Americas and look for signs of the bacteria in modern wildlife.
“This is only the beginning,” Bos said. “Every genome we find could change another part of history.”
Conclusion
The discovery that a rare type of leprosy was present in the Americas 4,000 years ago makes us rethink the story of infectious diseases in the New World. M. lepromatosis is not a foreign import; it may have been a silent, long-term threat that still exists in the shadows of modern medicine. As scientists keep looking at old bones and animals, we might find even more forgotten diseases that changed the course of human history in ways we don’t yet fully understand.
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Suhail Ahmed is a passionate digital professional and nature enthusiast with over 8 years of experience in content strategy, SEO, web development, and digital operations. Alongside his freelance journey, Suhail actively contributes to nature and wildlife platforms like Discover Wildlife, where he channels his curiosity for the planet into engaging, educational storytelling.
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