Daniel Danielssen. Portrait of Daniel Cornelius Danielssen (1815-94), Norwegian physician and leprosy pioneer. Danielssen worked in the Leprosy Hospital in Bergen, Norway. His book on leprosy in 1847 was a major advance in defining the disease. With C.W. Boeck, Danielssen made Bergen the dominant European centre for leprosy research. Erroneously, he always regarded leprosy as a hereditary disease. Leprosy is caused by a bacillus, Mycobacterium leprae, which is similar to the tuberculosis bacteria. The disease causes damage to nerves and a loss of sensation. This allows injuries to go unnoticed and the patient can become disfigured due to secondary infections.