The history books say Europeans brought leprosy to the Americas, but analysis of ancient DNA reveals that a form of the disease was present in Argentina and Canada much earlier
By Christa Lesté-Lasserre
29 May 2025
Leprosy can be caused by two species of bacteria, Mycobacterium leprae or Mycobacterium lepromatosis
nobeastsofierce Science/Alamy
A form of leprosy affected people in the Americas long before the arrival of Europeans, contrary to popular belief.
“The narrative around leprosy has been always been that it’s this awful disease that Europeans brought to America,” says Nicolàs Rascovan at the Pasteur Institute in Paris. “Well, our discovery changes that.”
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The vast majority of leprosy cases worldwide are caused by the bacterium Mycobacterium leprae. But in 2008, Xiang-Yang Han at the University of Texas MD Anderson Cancer Center and his colleagues discovered a second causative agent, M. lepromatosis, in two people from Mexico who had leprosy. Since then, scientists have found more cases of this pathogen in the US, Canada, Brazil and Cuba – as well as in four people in Singapore and Myanmar.
Wanting to know more about this understudied pathogen, Rascovan teamed up with Han and other researchers, as well as Indigenous communities, to analyse ancient DNA from 389 people who lived in the Americas before European contact.
They found M. lepromatosis in the remains of one person near the Alaska-Canada border and two others along the south-eastern coast of Argentina, all carbon-dated to about 1000 years ago. The bacteria’s genomes varied slightly, hinting at distinct strains separated by around 12,000 kilometres. “It spread so fast, on a continental level, in just a matter of centuries,” says Rascovan.