Leprosy

Leprosy, also known as Hansen's disease, is a chronic infectious disease caused by the obligate intracellular bacterium Mycobacterium leprae (and in some cases Mycobacterium lepromatosis). While it is an infectious disease rather than a purely genetic disorder, host genetic susceptibility plays a significant role in determining whether an exposed individual develops disease and which clinical form manifests. The disease primarily affects the skin, peripheral nerves, mucosa of the upper respiratory tract, and eyes. It has a remarkably long incubation period, typically ranging from 3 to 5 years but sometimes extending to 20 years. Leprosy presents across a clinical spectrum classified by the Ridley-Jopling system. At one end, tuberculoid leprosy (paucibacillary) features well-defined, hypopigmented or erythematous skin lesions with loss of sensation, thickened peripheral nerves, and a strong cell-mediated immune response limiting bacterial growth. At the other end, lepromatous leprosy (multibacillary) is characterized by widespread, symmetrical skin nodules (lepromas), diffuse skin infiltration, nasal congestion, and high bacterial loads due to poor cell-mediated immunity. Borderline forms exist between these poles. Nerve damage leads to sensory loss, muscle weakness, and deformities of the hands, feet, and face. Complications include plantar ulcers, claw hand, foot drop, lagophthalmos, and blindness. Immunological reactions (Type 1 reversal reactions and Type 2 erythema nodosum leprosum) can cause acute nerve damage and systemic inflammation. Treatment is highly effective with multidrug therapy (MDT) as recommended by the World Health Organization, combining dapsone, rifampicin, and clofazimine. Paucibacillary disease is treated for 6 months and multibacillary disease for 12 months. Early diagnosis and treatment prevent disability. Genetic susceptibility loci have been identified in several genes including HLA class II genes, TLR1, TLR2, PARK2/PACRG, NOD2, LRRK2, RIPK2, and others, underscoring the multifactorial nature of disease susceptibility. Despite being curable, leprosy remains endemic in parts of India, Brazil, Indonesia, and several other countries, with approximately 200,000 new cases reported annually worldwide.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

Common questions about Leprosy