leprosy or Hansen's disease hănˈsənz [key], chronic, mildly infectious malady capable of producing, when untreated, various deformities and disfigurements. It is caused by the rod-shaped bacterium Mycobacterium leprae, first described by G. Armauer Hansen, a Norwegian physician, in 1874. The mode of transmission is not fully understood. It is thought to be transmitted by nasal discharges and skin sores, and possibly also by contaminated objects and arthropods and by infected armadillos (which are also susceptible to the disease). Only 5% of those exposed acquire the disease. The onset is intermittent and gradual; symptoms may not appear until years after exposure. It is seldom fatal, but its involvement of the peripheral nerves destroys sensation and makes the patient prone to inadvertent injury.

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