Mycobacterium leprae bacteria. Light micrograph of M. Leprae bacteria (red) in a sample of nasal mucus. This Gram-positive rod-shaped bacteria is the cause of leprosy, or Hansen's disease. It has never been grown on culture media, suggesting that it has lost genes for independent survival and is now an intracellular parasite. Leprosy is a chronic disease of tropical and subtropical regions. It causes lesions on the skin and mucous membranes and damage to the peripheral nervous system that leads to loss of feeling. The numbness leads to frequent injuries and can result in deformities.