Leprosy is now called Hansen's Disease after Armauer Hansen the Norwegian who discovered the bacterium that caused it (Mycobacterium leprae) in Norway in 1873. In fact, it was … the very first bacterium that caused a human disease to be discovered.3 people found this useful.eprosy is now called Hansen's Disease after Armauer Hansen the Norwegian who discovered the bacterium that caused it (Mycobacterium leprae) in Norway in 1873. In fact, it was … the very first bacterium that caused a human disease to be discovered. 3 people found this useful.