Final Answer:
Gerhard Armauer Hansen discovered that the bacillus that causes leprosy is Mycobacterium leprae. Thus the correct option is A.
Step-by-step explanation:
Gerhard Armauer Hansen, a Norwegian physician, is credited with the discovery that the bacillus causing leprosy is Mycobacterium leprae. In the late 19th century, Hansen conducted extensive research on leprosy patients, examining skin lesions and identifying the specific bacterium responsible for the disease. In 1873, he successfully isolated the bacteria and later published his findings in 1874, establishing the connection between Mycobacterium leprae and leprosy. This discovery marked a significant milestone in the understanding of leprosy's etiology and laid the foundation for further research and treatment strategies.
Hansen's groundbreaking work was crucial in distinguishing leprosy as a bacterial infection, contributing to the broader field of microbiology. His meticulous observations and scientific rigor allowed him to make a conclusive link between Mycobacterium leprae and leprosy, dispelling earlier misconceptions about the disease's origin. Hansen's identification of the specific bacterium paved the way for advancements in diagnostic methods and therapeutic approaches. The naming of the causative bacterium after him, Mycobacterium leprae, recognizes his pivotal role in unraveling the microbiological aspect of leprosy, a contribution that remains significant in the history of medical science.