In a study published in Science, researchers revealed that the leprosy-causing bacterium Mycobacterium lepromatosis was present in the Americas for at least one thousand years before European settlement, altering our understanding of the disease's origins, according to Vice News.

For decades, historians and scientists assumed that Europeans brought leprosy to the Americas, much like smallpox. However, this study shows that Mycobacterium lepromatosis was already affecting American Indigenous communities over a thousand years ago.

The researchers examined over 800 samples, including 389 ancient and 408 modern DNA samples, with the cooperation of Indigenous communities. They found traces of Mycobacterium lepromatosis in thousand-year-old human remains in Canada and Argentina, including three pre-Columbian skeletons.

Biologist Nicolás Rascovan, head of the Microbial Paleogenomics Unit at the Pasteur Institute in France, led the investigation. An international team analyzed DNA from both modern patients and ancient remains across the Americas, reconstructing, analyzing, and dating the genomes of the bacteria taken from the samples.

"Some lineages of Mycobacterium lepromatosis appear to have been evolving in the Americas for over 9,000 years," the study notes, noting the diversity of pathogens and their complex relationship with humans throughout history.

Geneticist Maria Lopopolo from the Pasteur Institute in France stated that traces of the Mycobacterium lepromatosis bacterium were found in thousand-year-old human remains in Canada and Argentina. Comparisons between the samples showed that the bacterial genomes were of distinctive branches of the lepromatosis species at each end of the continent.

Despite its ancient presence, Mycobacterium lepromatosis was only discovered in 2008 when doctors in Mexico found it in a leprosy patient. This suggests that there may be still undiscovered types of leprosy and unexplored animal hosts.

"Mycobacterium lepromatosis is still largely a mystery because leprosy-causing bacteria do not grow in petri dishes and prefer to hijack human cells," the researchers explained. The difficulty in studying leprosy-causing bacteria likely explains why their history in the Americas has been easy to overlook.

Leprosy is a chronic infectious disease caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis, affecting the skin, peripheral nerves, mucous membranes of the upper respiratory tract, and other organs. Leprosy has been infecting humans for thousands of years.

Today, leprosy can be treated with antibiotics, but ancient sufferers weren't so fortunate. Currently, approximately 200,000 new cases of leprosy are detected each year.

While Mycobacterium leprae, the more well-known type of leprosy, likely arrived in the Americas via European colonists, its sibling Mycobacterium lepromatosis was already affecting American Indigenous communities over a thousand years ago.

"The diversification happened probably independent of humans," said Rascovan, as reported by Deutsche Welle.

The arrival of the first European fleets to the Americas in 1492 marked the introduction of new diseases, including leprosy in the form of Mycobacterium leprae. This devastated Indigenous communities and intensified the impact of pathogens that were already circulating before colonization.

"Europeans had a very important impact by bringing this new species [leprae] that was absent in America," said Rascovan. He hopes the presence of Mycobacterium lepromatosis in the archaeological record will improve understanding of pre-colonial disease, especially in the absence of written records.

The study helps understand modern cases of leprosy, especially how it could make the jump from animals like squirrels to humans. "Our work is giving the kick start to really start analyzing, monitoring and understanding the diversity of natural reservoirs [disease carriers]," Rascovan added.

Scientists are now prompted to work on piecing together the real leprosy family tree. This discovery suggests that there may be still undiscovered types of leprosy and unexplored animal hosts. Monitoring the disease and preventing spillovers from animals to humans should be a priority.

Leprosy presents as multiple numbing skin lesions. If left untreated, it can result in nerve damage, muscle weakness, paralysis, and blindness.

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