Scientists say a species of bacteria rewrites the history of when an infectious and potentially deadly disease first arrived in the Americas. And it was long before the arrival of European explorers.

Researchers from the Institut Pasteur in Paris, France, with help from a U.S. university, recently announced in a news release that a second species of bacteria is also responsible for the disease known as leprosy, or Hansen's disease, in the Americas. 

In years past, many believed that the bacterium known as Mycobacterium leprae caused leprosy and that it was only spread in America by early European explorers and settlers.

However, the revelation of a second bacterium puts that theory of blaming the settlers on its head, as an existing strain was already on the continents calling the New World home.

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The Institut Pasteur in Paris announced that they have found a second species of bacteria responsible for the disease in the Americas. (Netflix/Paramount)

The bacterium Mycobacterium lepromatosis existed and infected humans for 1,000 years prior to Europeans arriving, researchers say.

Dr. Maria Lopopolo, the first author of the study and researcher at the Laboratory of Microbial Paleogenomics at the Institut Pasteur, said it changes everything about leprosy in the Americas.

"This discovery transforms our understanding of the history of leprosy in America. It shows that a form of the disease was already endemic among Indigenous populations well before the Europeans arrived," she said in the release.

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Scientists at the Institut Pasteur in Paris, alongside the French National Centre for Scientific Research and the University of Colorado, conducted the study. (iStock)

The study — led by scientists from the Laboratory of Microbial Paleogenomics at the Institut Pasteur, alongside the French National Center for Scientific Research, and the University of Colorado in the U.S. — began after Mycobacterium lepromatosis was found in a Mexican patient in 2008, and red squirrels in the British Isles in 2016.

Using advanced genetic techniques to reconstruct the genomes of Mycobacterium lepromatosis from ancient individuals from Argentina and Canada, scientists found that the two strains from the different regions were genetically close in the Mycobacterium genome family tree, meaning that the bacteria spread rapidly throughout the continent.

The release stated that the results confirmed that Mycobacterium lepromatosis had already spread throughout North and South America.

The researchers were able to study over 800 different DNA samples from ancient human remains and recent medical cases showing signs of leprosy. (iStock)

Researchers worked in collaboration with indigenous communities, various international institutions and archaeologists, according to the release, and were able to study over 800 DNA samples from ancient human remains and recent medical cases showing signs of leprosy.

Nicolás Rascovan, the lead author of the study at the Institut Pasteur, said that the research proves that human history can be changed.

"We are just beginning to uncover the diversity and global movements of this recently identified pathogen," he said. "This study allows us to hypothesize that there might be unknown animal reservoirs."

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The Centers for Disease Control and Prevention (CDC) says leprosy can affect the nerves, skin and eyes of patients, and is treated with antibiotics. Up to 225 people in the U.S., and 250,000 around the world, contract Hansen's disease, according to the CDC.

Nick Butler is a reporter for Fox News Digital. Do you have any tips? Reach out to Nick.Butler@Fox.com.