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Clinical, immunological, and genetic aspects in leprosy

Leprosy is a chronic infection caused by Mycobacterium leprae. It affects the skin and peripheral nerves and can cause irreversible chronic disabilities. The worldwide registered number of cases in 2009 was 213,036. This review discusses clinical aspects of the disease, including leprosy reactions and neuronal damage, as well as immunological and immunogenetic aspects influencing disease susceptibility and outcome. The cardinal signs of leprosy are skin lesions with altered sensation, thickened peripheral nerves, and presence of alcohol acid‐resistant bacilli in skin biopsy or lymph. Confirmatory examinations include (1) bacteriological examination, which allows patients' classification into two operational groups, multibacillary (MB) and paucibacillary (PB); and (2) histopathological examination, which permits stratification in different clinical forms. These clinical forms differ not only by histopathology but also according to the host's immune response to M. leprae. These forms comprise the extremes of (1) tuberculoid leprosy (TT), with a specific Th1 response and control of M. leprae multiplication; (2) lepromatous leprosy (LL) without Th1 response and preserved Th2 response; and (3) the interpolar clinical forms, borderline tuberculoid (BT), borderline borderline (BB), borderline lepromatous (BL), and indeterminate form (IL). Appropriate treatment is based on smear examination or the number of lesions at diagnosis. In the evolution of leprosy, acute inflammation, known as reactions, may occur during or after treatment. These reactions are classified into two main types: the type I reaction or reversal reaction (RR), and the type II reaction or erythema nodosum leprosum (ENL). The role of innate immune response to control the infection is supported by immunological and genetic studies. Drug Dev Res 72:509–527, 2011. © 2011 Wiley‐Liss, Inc.