Which bacterium causes leprosy, a chronic infection also called Hansen’s disease?

Mycobacterium leprae causes leprosy, a chronic infection also called Hansen’s disease.

The bacterium was identified in 1873 by Norwegian physician Gerhard Armauer Hansen, making it the first bacterium clearly linked to a human disease. It primarily affects the skin and peripheral nerves, and untreated infection can lead to loss of sensation and tissue damage.

M. leprae is an acid-fast bacterium with a lipid-rich cell wall, a feature it shares with other members of the genus Mycobacterium. It grows extremely slowly and has not been successfully grown in ordinary artificial laboratory culture, making research unusually difficult.

Leprosy is not highly contagious, and prolonged close contact is generally required for transmission. Modern treatment uses combinations of antibiotics. Mycobacterium lepromatosis is another recognized cause of leprosy, so the disease does not have only one bacterial species worldwide.