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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.
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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
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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
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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.
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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 ...