Leprosy in America Might Not Have Been Europe’s Fault After All

Leprosy had already been in America long before Europeans were coughing on each other in wooden ships bound for the New World.

According to a recent study in Science, researchers discovered that Mycobacterium lepromatosis, one of two bacteria known to cause leprosy, was lurking in the Americas long before Europeans crossed the Atlantic.

For decades, historians and scientists assumed Europeans brought leprosy to the Americas, like they did smallpox. And while Mycobacterium leprae, the more famous kind of leprosy, did likely arrive via colonists, its sibling, M. lepromatosis, was already creeping through American Indigenous communities over a thousand years ago.

Led by Nicolas Rascovan of the Pasteur Institute, an international team dove into DNA from both modern patients and ancient remains across the Americas. The researchers found three pre-Columbian skeletons from Canada and Argentina that tested positive for M. lepromatosis. Even wilder, some bacterial lineages appear to have been evolving here for over 9,000 years.

Leprosy Infected the Americas Differently Than We Thought

Despite how old this pathogen is, M. lepromatosis was only discovered in 2008. It’s still largely a mystery, because leprosy-causing bacteria are weirdly antisocial in the lab. They refuse to grow in petri dishes, preferring instead to hijack human cells. That’s made them extremely hard to study, likely explaining why their history in the Americas is been so easy to overlook.

Now, with evidence that this disease has deep American roots and unexplored animal hosts, scientists are working to piece together the real leprosy family tree. Cataloging leprosy’s past will help us better understand its future.

Maybe our understanding of how it’s been able to evade us for so long can help us find a pathogen that’s been lingering around us silently for years.