Ancient American Origins of Leprosy Pathogen Redraw Global Disease History

For decades, scientists believed leprosy was a disease of the Old World, introduced to the Americas around 500 years ago by European colonizers and African slaves. The disease was traditionally attributed solely to Mycobacterium leprae. However, the 2008 discovery of a second leprosy-causing bacterium—Mycobacterium lepromatosis—in Mexico raised new questions about the disease's history.

Subsequent findings expanded the mystery. In 2016, M. lepromatosis was detected in British red squirrels, and in 2018, traces were found in ancient DNA from a human skeleton in western Canada, dating back over a thousand years. These discoveries hinted that the bacterium may have existed in the Americas well before European contact.

Now, a new study confirms this theory. Researchers from the Pasteur Institute in France screened ancient DNA databases and identified M. lepromatosis in skeletal remains from two pre-Columbian archaeological sites in Canada and Argentina, suggesting the pathogen once had a broad distribution across the continent.

Despite leprosy's known symptoms—severe skin lesions, bone deformities, and nerve damage—such indicators had been largely absent in pre-Columbian remains, reinforcing the earlier belief that the disease arrived with Europeans. The new genetic evidence overturns this assumption.

Further analysis by Colorado State University scientists revealed that M. lepromatosis still infects modern leprosy patients, especially in Mexico. Genomic data suggests the bacterium originated in the Americas around 9,000 years ago, diverging from M. leprae as far back as 1 million years. Its mode of transmission remains unclear, possibly linked to ancient human migrations or native wildlife.

This discovery reshapes our understanding of leprosy's global history and underscores the power of ancient DNA research. With thousands of new leprosy cases reported worldwide each year, these insights may prove crucial for improving prevention and treatment strategies.