A New History of Leprosy: The Global Health Implications of the Discovery of Mycobacterium lepromatosis

These are the abstracts of papers presented at the 2013 meeting of the American Association for the History of Medicine in Atlanta, GA. Mycobacterium lepromatosis, a second species of leprosy, was discovered in 2008. By 2012, subsequent research had confirmed that its age as a "sister" species to M. leprae (previously the only known cause of leprosy in humans, which had been discovered by Hansen in 1873) was likely very old. This panel addressed the question of how historical questions might be formulated to begin to discern this disease in human populations and the geography of its spread. Note that the "out of Africa" narrative that this abstract proposed when first drafted in 2012 has been overturned by subsequent work; it is now more likely that M. leprae arose near the Pacific Rim. The long-term origins of M. lepromatosis as a human disease have yet to be determined. In 2025, two separate studies announced the identification of ancient DNA of M. lepromatosis, confirming its presence in the Americas for at least the last 10,000 years.