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INTRODUCTION

KEY POINTS

  • Leprosy is a mycobacterial infection that affects the skin and the peripheral nerves.

  • There are over 200,000 new cases of leprosy diagnosed every year around the world.

  • Various skin symptoms are associated with the disease depending on the immune reaction of the host (patient), including hypopigmentation, erythema, and nodules.

  • Multidrug therapy, which is a combination of dapsone, rifampicin, and clofazimine, effectively cures the disease and is recommended as the first-line therapy by the World Health Organization.

  • Deformities as a consequence of the disease lead to social discrimination and stigma and, hence, the need for early detection and treatment.

Leprosy is a chronic bacterial infection caused by the intracellular microorganism Mycobacterium leprae. The bacteria have affinity for the peripheral nerves and skin, resulting in neuropathy and skin symptoms, which are cardinal manifestations of the disease. The diagnosis of this disease may be a challenge due to a wide variety of manifestations that are determined by the interplay between the bacilli and host immune responses, which eventually determine the clinical spectrum of the disease. If not treated early, the progressive nature of this chronic infectious disease may cause deformities of the face and limbs, loss of eyesight, and other long-term complications.

EPIDEMIOLOGY

Leprosy is seen most commonly in people with skin of color predominantly in developing countries in tropical and subtropical regions including India, Brazil, and Indonesia.1 Socioeconomic factors, including poverty, overcrowding, and poor sanitation, are known to play a significant role in the increased disease prevalence in these regions.

Sporadic cases encountered in developed nations often occur among immigrants from countries where the disease is endemic.

ETIOLOGY AND PATHOGENESIS

M. leprae, the lepra bacillus, an acid-fast organism, was first discovered by G.H. Armauer Hansen in the year 1873. The organism is approximately 0.2 μm in width and 8 μm in length [Figure 66-1]. It grows best at a temperature around 31°C; thus, it thrives in cooler areas of the body such as the earlobes, nose, and testicles, and areas where the peripheral nerves are close to the skin. It is a slow-growing organism that needs 11 to 13 days to multiply. Otherwise, many of the characteristics of the bacilli are still unknown because the organism cannot be cultured in any laboratory media. In animal models, limited multiplication can be observed in the nude mouse foot pads.2

FIGURE 66-1.

Mycobacterium leprae (skin slit smear, Ziehl-Neelsen stain, ×1000).

Nonetheless, recent advances in genome sequencing have contributed to the better knowledge of the disease. The first genome sequence of M. leprae, completed in 2001, revealed that only half of the small genome contains protein-coding genes, whereas the remainder consists of pseudogenes and noncoding regions.3 The number of pseudogenes is ...

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