Chapter 271

Leprosy is a chronic infectious disease caused by Mycobacterium leprae, an acid-fast bacillus (AFB). It was first recognized by Hansen in 1873 in Bergen, Norway, while examining smears from lepromas of Norwegian patients. Notably, the organism was the first reported bacterium causing chronic disease in humans that principally affects the cooler parts of the body, especially the skin, upper respiratory tract, testes, eyes, and superficial segments of peripheral nerves.1,2 The stigma suffered by patients with leprosy has historically been severe. For a review of the history of leprosy refer to the electronic text. Because of the stigma of leprosy, the physician must carefully consider the social implications of a diagnosis of leprosy, especially in children.

### Epidemiology

In 1999, the World Health Organization (WHO) reported that approximately 800,000 patients were being treated for active leprosy, with 738,000 newly diagnosed cases. By 2006, the numbers had dropped to 225,000 and 259,000, respectively.3 However, many authorities consider that the total global prevalence of patients with active leprosy is much higher (1.5–2 million) and that new case rates are not necessarily rapidly declining.4,5 The stigma of the disease and inefficiency in health care delivery systems contribute to this disparity in statistics.6

The highest prevalence of leprosy is in tropical Africa, South America, and Southeast Asia. Approximately 73% of all patients live in Southeast Asia (65% in India), 12% in Africa, and 8% in the Americas.1 Approximately 6000 patients with a history of leprosy resided in the United States. Most of these patients are immigrants, but a few indigenous patients regularly come from Hawaii, Louisiana, Texas, and other southeastern states.70,71

Geographic, ethnic, and socioeconomic factors may contribute to the spread of leprosy by affecting the number of untreated or ineffectively treated bacillary-positive patients and the opportunities for exposure. Several leprosy epidemics have occurred in nutritionally debilitated populations, although there is still no convincing evidence that the prevalence of leprosy is unusually high in chronically malnourished populations.73,76,77 The percentage of patients who harbor large numbers of bacilli, generally those with lepromatous leprosy, is related to ethnic background. In some Asian populations, for example, 50% or more of those with leprosy have lepromatous leprosy; in Africans, this figure is 5% to 10%. In adults, leprosy occurs more commonly in men than in women (2:1–3:1); in children, the sex ratio is approximately 1:1.

Genetic factors likely influence the susceptibility of some individuals to leprosy, as well as the form of disease. Genome-wide screening in various populations has found associations with leprosy susceptibility on chromosome 10p13, near the gene for mannose receptor C, a phagocytic receptor on macrophages, on chromosome 6, within the major histocompatibility complex (MHC),89 and on the gene for tumor necrosis factor (TNF).90 Polymorphisms in the “promoter regions” of the IL-10 and TNF genes have also been ...

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