New Insights on the History of Leprosy in the Americas

For quite some time, historians thought that leprosy was brought to the Americas by European colonizers. However, recent research challenges this view, indicating that Indigenous Americans might have been affected by the disease long before European contact.

The disease is primarily caused by a bacterium known as Mycobacterium leprae, which researchers still believe was introduced to the continent by Europeans. Yet, it appears another, less widely recognized bacterium was already present.

A study conducted by an international team revealed the existence of Mycobacterium lepromatosis, another type of leprosy-causing bacterium, in ancient human remains found in Canada and Argentina, dated to at least a thousand years ago.

“This finding changes how we perceive the history of leprosy in America,” notes genomicist Maria Lopopolo from the Institut Pasteur in France. She emphasizes that a variant of this disease was already endemic among Indigenous communities well before the arrival of Europeans.

M. lepromatosis was first identified in a patient in the US in 2008 and has also been detected in red squirrels (Sciurus vulgaris) in the UK. Researchers propose that this bacterium may have traveled from the US to the UK during the 19th century.

Working alongside local Indigenous groups to manage ancestral remains, the team analyzed DNA from 389 ancient and 408 modern human samples. Their findings allowed them to construct a genetic family tree of leprosy bacteria.

Despite the vast distances between the ancient samples from Canada and Argentina, the genetic similarities were striking, indicating a rapid spread of M. lepromatosis across the Americas.

The researchers estimate that various strains of M. lepromatosis diverged from a common ancestor over 9,000 years ago. Given such a long evolutionary timeline, they suspect there are likely many more unknown forms of the bacteria still waiting to be discovered in the Americas.

“We are just scratching the surface of understanding the diversity and global movement of this recently found pathogen,” says biologist Nicolás Rascovan from the Institut Pasteur. He suggests that unknown animal reservoirs may also exist.

This information adds a valuable dimension to our understanding of the history of the Americas and leprosy. It provides researchers with critical insights into how the disease has evolved over time.

Infectious diseases have significantly influenced the narratives of North, South, and Central America, particularly with the arrival of Europeans who introduced a myriad of new pathogens that Indigenous populations were not equipped to handle.

Now, it’s clear that the story of leprosy is more intricate than previously thought. Every year, about 200,000 new instances of the disease are documented globally, though it can be treated successfully with modern medication.

“This research highlights how both ancient and modern DNA can reshape our understanding of human pathogens and enhance our grasp of the epidemiology of today’s infectious diseases,” Rascovan concludes.

This research has been published in Science.