Leprosy skin lesion. Light micrograph of a section through human skin suffering from lepromatous leprosy. Leprosy is a chronic infectious disease caused by the bacterium Mycobacterium leprae. Symptoms of lepromatous leprosy are disfiguring skin lesions and high numbers of bacilli in the infected tissues. Lepromatous lesions may be flat (macular), raised (papular) or nodular. Damage to the peripheral nerves also leads to sensory loss in the skin. The surface cornified layer of the skin is at top. Beneath this is the epidermis, beneath which is the dermis. During infection the dermis becomes packed with macrophages with vacuolated cytoplasm.