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  • Definition: A chronic granulomatous disease affecting mainly the skin and nerves caused by the obligate intracellular pathogen Mycobacterium leprae.

  • Involvement: Primarily the skin and nerves, but causing sequelae to a wide range of tissues and systems including eyes, upper respiratory tract, lymphoid tissue, testicles, muscles, and bones.

  • Diagnosis: Based on clinical signs and symptoms, hallmarks include loss of sensation within skin lesions, nerve swelling or pain, or demonstration of acid-fast bacilli in skin smears or biopsies.

  • Incidence: 214,783 new cases detected worldwide in 2016, essentially unchanged for the last 4 years. More than 80% of all new cases are detected in only 3 countries—India, Brazil, and Indonesia.

  • Long-term morbidity: Despite the global use of multidrug therapy in use since the mid-1980s, up to 30% to 50% of all leprosy patients will experience some type of reactional episode that may result in a permanent neurologic deficit or disability.

  • A clinical challenge: The long incubation time prior to the slow development of diverse symptoms (3-7 years postinfection), the very low rate of disease progression in infected individuals, and issues with misdiagnosis all create challenges to the development of ways to interrupt transmission.

  • An immunologic spectrum of disease: Understanding what genetic factors and the interplay of innate and adaptive immune responses of the host that leads to resistance or susceptibility to disease are critical in developing novel treatment approaches.



Leprosy is a chronic granulomatous infection caused by Mycobacterium leprae, that infects mucous cutaneous tissues and peripheral nerves, leading to loss of sensation on the skin—with or without dermatologic lesions—and the development of incapacities during the progression of the disease. WHO states that any individual in endemic countries presenting skin lesions with definite sensory loss or positive skin smears may be diagnosed with leprosy.1


Leprosy is one of the oldest diseases known to afflict mankind. Gerhard Armauer Hansen, a Norwegian physician, was the first to describe the M. leprae bacillus in 1873, identifying the first bacterial pathogen associated with human disease. The name Hansen disease is used in some countries, like Brazil, to lessen the stigma associated with the common name. The characteristic destructive changes that lead to disfigurement, deformity, and disability were among the hallmarks of the disease that allowed it to become stigmatized in ancient times.2 Speculations about the existence of leprosy in ancient India, Egypt, and China have been proposed, with the earliest paleopathological evidence found in 4000-year-old bones from the Balathal burial site in Rajasthan, western India.3 The first use of molecular techniques using polymerase chain reaction (PCR) to detect M. leprae DNA specific sequences in ancient bones dated to AD 600 was described in 1994.4 PCR was used to identify M. leprae DNA in 1st century CE bones from the Tomb of the Shroud ...

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