Leprosy’s Ancient Origins in the Americas
A recent study has challenged the conventional wisdom surrounding the origins of leprosy in the Americas. Contrary to popular belief, a form of leprosy was found to have affected people in the Americas long before the arrival of Europeans.
The majority of leprosy cases worldwide are caused by the bacterium Mycobacterium leprae. However, in 2008, a second causative agent, Mycobacterium lepromatosis, was discovered by Xiang-Yang Han at the University of Texas MD Anderson Cancer Center. This pathogen has since been found in various countries, including the US, Canada, Brazil, Cuba, Singapore, and Myanmar.
To further study this understudied pathogen, researchers, including Nicolàs Rascovan from the Pasteur Institute in Paris, analyzed ancient DNA from 389 individuals who lived in the Americas before European contact. Surprisingly, they found evidence of Mycobacterium lepromatosis in the remains of individuals dating back approximately 1000 years.
The analysis revealed that the bacteria’s genomes varied slightly, indicating distinct strains separated by thousands of kilometers. This suggests that Mycobacterium lepromatosis spread rapidly across the continent in just a few centuries.
Modern cases of Mycobacterium lepromatosis in the US and Mexico showed that contemporary strains are essentially clones, with minor changes since ancient times. However, the study also identified a rare, ancient strain in a modern individual that had not been found in archaeological remains, indicating the presence of at least two distinct lineages of the pathogen in North America today.
Genetic data showed that Mycobacterium lepromatosis and Mycobacterium leprae split from a common ancestor over 700,000 years ago. The study also revealed that one lineage of the pathogen mutated about 3000 years ago, leading to an infection in red squirrels in the UK and Ireland.
Modern cases of Mycobacterium lepromatosis primarily affect blood vessels, particularly in the legs and feet, causing skin damage and potentially deadly complications. This differs from Mycobacterium leprae, which mainly targets the nerves. The research also highlighted the challenges in identifying leprosy in ancient remains from the Americas, as the disease may not present classic bone damage symptoms.
The study has significant historical implications, prompting a reevaluation of leprosy’s history in the Americas. It also underscores the importance of surveillance and global efforts to map leprosy strains, especially as the disease re-emerges in some parts of the world and antimicrobial resistance poses challenges to treatment.
