Leprosy was present in the Americas before the arrival of European colonizers
This is what a study published on May 29 in the journal Science shows, involving more than 50 researchers from France, North America, and South America. The study sheds new light on the precolonial history of infectious diseases on a continent that remained isolated from the rest of the world for thousands of years.
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Affecting over 200,000 new people each year, leprosy—characterized by skin lesions and primarily caused by Mycobacterium leprae, known since the 19th century—was long thought to have been introduced to the Americas by Europeans and responsible for the majority of cases on the continent. But it is a second bacterium, Mycobacterium lepromatosis, discovered only in 2008 in Mexico, that is the focus of this study.
Until now, scientists had sequenced this species’ genomes only from Mexican patients and red squirrels in the British Isles (Ireland, England, Scotland), identifying two lineages.
“It was still impossible to determine whether the pathogen had been imported into the Americas from Europe or vice versa,”
explains Nicolas Rascovan, head of the microbial paleogenomics unit at the Institut Pasteur, who coordinated the study.
A first discovery came in 2017: using ancient DNA data, researchers identified the genetic signature of the bacillus in an individual who lived in present-day Canada around 1,300 years ago.
“That was a fairly significant finding, suggesting that the bacterium might have existed before the arrival of Europeans,”
he says. But more contextual data was lacking.
Beginning in 2020, the team analyzed more than 800 ancient and modern samples.
Maria Lopopolo, the study’s lead author and then a doctoral student in the lab, insisted on also studying remains from the southern part of the continent.
“When she showed me her results, I initially thought she had made a mistake. But she was right: she had found a case of leprosy in Argentina dating back 900 years,”
says Rascovan. Suddenly, it was clear that the pathogen had been hiding in plain sight.
A Link Between Indigenous Communities
The two lineages—Canadian and Argentinian—likely shared a common ancestor 2,000 years ago, suggesting the bacterium spread across the continent over the course of several centuries.
“That’s very fast for a continent that spans 10,000 kilometers,”
notes the scientists.
In total, 26 DNA samples (3 ancient and 23 modern) out of the 800 analyzed contained the leprosy bacillus and were usable. They helped identify three new lineages within the species Mycobacterium lepromatosis, in addition to the two already known.
“The findings presented in this study are remarkable,”
says Emmanuelle Cambau, researcher at the National Reference Center for Mycobacteria and for Mycobacteria Drug Resistance, and member of the WHO leprosy control group. The work opens up new research avenues in other regions:
“Some cases of leprosy caused by Mycobacterium lepromatosis have also been observed in Asia. More study is needed to determine which branch they belong to and identify ancestral sources that might explain their origins.”
A Rare Example of Ethical Archaeology
Rare in ancient DNA research, the communities involved—particularly in Argentina—were informed of the historical relevance of their populations.
“That’s why it’s important to construct narratives that are not only scientifically accurate but also socially meaningful,”
says Rascovan.
In a WhatsApp voice message sent from Las Grutas, a coastal town in Argentina, a local representative expressed how the “very fluid” relationship with the scientists and the “exchange of knowledge” enabled this work.
“It is essential that we be included when research is done on our lands, and that we stop being seen through a distorted vision of science, as if we were mere study subjects instead of active participants,”
he declared.
Global Connection Through the Microbe
For Indigenous groups like the Mapuche community, the spread of the microbe across the entire continent resonates with their worldview. One of their philosophies, called Traun Kutral, suggests that all living beings are interconnected.
“These similarities between species and across the territory of the Mapu [the land] don’t surprise us—they even seem logical,”
a member concluded in his native language.
European Archaeology Days
Three kilometers south of Auxerre (Yonne), at a site known as Sainte Nitasse, a team from the French National Institute for Preventive Archaeological Research (INRAP) has uncovered a Roman villa. The site will be open to the public on Sunday, June 15, from 10 a.m. as part of European Archaeology Days, running from June 13 to 15. The event will include numerous excavation sites, exhibitions, workshops, demonstrations, and conferences. It comes amid broader concerns: on June 12, archaeologists are expected to protest in Paris against funding cuts and controversial projects.
