Hansen's disease.
Earlier this year, I visited the University of Bergen to give a lecture, and found that the department where I was speaking was in one of Bergen's former leprosy hospitals. Norway is now very wealthy, so it is a shock to discover that it was one of the poorest countries in Europe until well into the twentieth century, and leprosy was endemic there. Bergen still takes pride in G.H. Armauer Hansen (1841–1912), the local physician who first identified Mycobacterium leprae , and whose name became an eponym for the disease.

Hansen's achievements in defeating leprosy were prodigious.1 He began his career with detailed population research, and used it to show that leprosy was neither a hereditary disease nor due to poor living conditions alone, thus disproving two ideas that were common at the time. He then used Norway's national leprosy register to demonstrate that isolating patients led to a decline in the incidence of the disease, suggesting that leprosy was almost certainly infectious. No-one had previously shown that a chronic …