Leprosy occurs naturally only in humans and is caused by infection with Mycobacterium leprae. Known also in the twentieth century as “Hansen’s disease,” after the Norwegian microbiologist A. G. H. Hansen who first isolated the microorganism in 1873, true leprosy is a chronic, debilitating, and disfiguring infection. However, the long history of disease attributed to leprosy undoubtedly includes a broad range of skin and systemic afflictions that only resembled leprosy symptoms.

The leprosy bacillus multiplies quite slowly, usually in the sheaths of peripheral nerves. Losing sensation in discrete, patchy areas of the skin is often the earliest, but ignored, symptom of infection. Lacking adequate innervation, the affected dermis can be damaged without evoking a pain response as, for example, by a burn or a cut. Repair of the tissue is then hindered by poor regulation of local blood supply. Hence, secondary infection and inflammation of an involved area are common, leading to scarring and callusing of surviving tissues. This long process can result in the loss of fingers, toes, nasal tissue, or other parts of the body frequently exposed to the elements. A “bear claw” foot or hand becomes one of the characteristically maiming and stigmatizing features of the leper. Involvement of the nasal cartilage and vocal cords, common sites for the organism’s growth, leads to profound disfiguration of the center of the face and also to the raspy, honking voice described in some historical accounts of true leprosy.