HANSEN'S DISEASE - Leprosy is a chronic granulomatous infection of humans by the bacterium Mycobacterium leprae. Leprosy affects the superficial tissues, especially the skin and peripheral nerves. It is estimated that there are between 10 and 20 million persons affected with leprosy in the world. Leprosy is most common in tropical climates (even as close as Mexico), but quite rare in the United States. Ninety percent of the cases diagnosed in the U.S. have occurred in immigrants from leprosy-endemic countries. Some sporadic reports of leprosy have come out of Hawaii and the Gulf Coastal areas of the U.S.