What Would Constantine Do? A Post on Science and Migration in Honor of World Leprosy Day 2026

Part of an annual series of essays to honor World Leprosy Day, this blogpost for 2026 uses the 11th-century medical translator, Constantine the African, as a focal point to think about new developments in the history of leprosy as a global disease. New research has confirmed that the 2nd species of leprosy discovered in 2008, Mycobacterium lepromatosis, does in fact have a very deep history in the Americas, going back at least 10,000 years. This history can now be compared with that of M. leprae, the leprosy that has moved through Afro-Eurasia for about 5-6000 years. As geneticists, bioarchaeologists, and historians learn more about the evolution of pathogens, we also learn more about how to think about the connections between pathogens, animals, and the many landscapes humans have migrated through. Science, too, is recognized as part of the adaptations that humans have made to address infectious diseases. Constantine, an immigrant from North Africa, was recognized by his contemporaries as having shared the gift of medical science with medieval Europe.