[Gerhard Henrik Armauer Hansen--still of current interest].
Armauer Hansen described his first observation of Mycobacterium leprae on 28 February 1873 in detail. His discovery of the leprosy bacillus was the result of a logical process in which distinct stages can be clearly seen. The first step was clinical, and established criteria for leprosy as "a specific disease". The second stage was epidemiological. Contrary to the main view favouring a genetic basis, these observations convinced him of the infectious nature of the disease. The third stage was the search for the bacillus. His basic observations were reproduced, as documented. Armauer Hansen afterwards tried to fulfill Koch's postulates, in order to prove that the bacillus was the causative agent of leprosy. His second main contribution is the work on leprosy control, emphasizing isolation to contain the infection. The subsequent decline of leprosy in Norway differs from the trend in many developing countries, where leprosy has remained an important public health problem. In recent years Norwegian medical research has made significant contributions to leprosy research, in the field of epidemiology in Bergen, and through immunological studies of the disease originating from the Armauer Hansen Research Institute in Addis Ababa, Ethiopia.