Identification of Mycobacterium leprae

In 1873 the Norwegian physician Gerhard Armauer Hansen announced that he had found a rod-shaped microorganism in the tissues of people with leprosy, the bacterium now named Mycobacterium leprae. It was the first bacterium to be identified as a cause of disease in humans, and it undercut the older view that leprosy was inherited or arose from foul air. Hansen worked in Bergen, reasoned from epidemiological studies that the disease was communicable with a specific cause, and made the observation with a new and better microscope, although he did not at first recognize the objects as bacteria and received little support. The organism cannot be grown in cell-free laboratory media, which weakened his claim, and Albert Neisser, who stained the bacteria in 1880, also announced the discovery as his own. Mycobacterium leprae is an acid-fast, rod-shaped bacterium that damages the peripheral nerves, and the disease it causes is now called Hansen's disease.