Leprosy in the Global Middle Ages: A Slow Pandemic. A Post in Honor of World Leprosy Day 2025

This essay was written to honor World Leprosy Day 2025, 26 January. I chose as the theme for this year evidence for leprosy's global circulation, much of which had happened during the Middle Ages. In fact, recent genetic work suggests that leprosy may have already crossed the Pacific by around 1250 CE. Drawing on historical, bioarchaeological, and phylogenetic findings, this essay suggests that the current-day global distribution of leprosy might be better understood if we also consider its medieval history--which, we know now, likely included transmission by animals as well as humans.