Leprosy.

Yes. WHO multidrug therapy (MDT) cures leprosy completely — 6 months for paucibacillary and 12 months for multibacillary disease. Cure rates exceed 98% in completed courses, and patients become non-infectious within days of the first rifampicin dose. MDT is supplied free of charge by WHO globally.

Leprosy is far less contagious than commonly believed. Over 95% of people are naturally immune. Transmission requires prolonged close contact (usually household-level) with an untreated multibacillary case, most likely via nasal mucosal shedding.

Leprosy spreads through prolonged close contact with an untreated multibacillary case, primarily via nasal droplets shed in the months to years before diagnosis. Household contacts have 5-10 times higher risk than the general population.

Early leprosy typically presents as one or a few pale or reddish patches on the skin with reduced or absent sensation when tested with light touch. Advanced multibacillary leprosy may show numerous symmetric lesions, eyebrow loss, nasal congestion, and thickened palpable peripheral nerves.

Diagnosis is clinical, based on WHO criteria: a hypopigmented skin lesion with sensory loss, a thickened peripheral nerve with deficit, or acid-fast bacilli on slit-skin smear. Skin biopsy and PCR confirm the diagnosis. In endemic regions, trained leprosy workers can often diagnose at first visit.

Multidrug therapy is the WHO standard regimen for leprosy: rifampicin once monthly, clofazimine daily plus a monthly larger dose, and dapsone daily. Paucibacillary leprosy is treated for 6 months; multibacillary leprosy for 12 months.

Paucibacillary leprosy (1-5 lesions, smear-negative) is treated for 6 months. Multibacillary leprosy (6 or more lesions or smear-positive) is treated for 12 months.

Untreated leprosy can damage peripheral nerves, leading to sensory loss, muscle weakness, and deformity (claw hand, foot drop, facial paralysis). With early MDT, most cases avoid permanent deformity.

WHO documented approximately 180,000 new cases globally in 2023. India, Brazil, and Indonesia together account for roughly 80% of new cases. Other notable endemic countries include Bangladesh, Nepal, Myanmar, the Philippines, Ethiopia, the Democratic Republic of the Congo, and Madagascar.

Yes. About 150-200 new cases are reported annually in the US, roughly 30% in patients with no foreign travel — most often linked to armadillo exposure in Louisiana, Texas, Florida, and Mississippi. The National Hansen's Disease Program in Baton Rouge provides free treatment and consultation.

Leprosy reactions are sudden inflammatory episodes during or after MDT, caused by immune response to the bacteria. Type 1 (reversal) reactions inflame existing skin lesions and nerves, risking permanent damage; Type 2 (erythema nodosum leprosum) causes painful tender nodules with fever.

Yes. Approximately 7% of new cases globally in 2023 were in children under 15 — an indicator of ongoing community transmission. Children typically present with paucibacillary disease. WHO weight-adjusts MDT doses for pediatric patients.

BCG vaccination provides partial protection against leprosy — roughly 50-60% efficacy in pooled studies, though it varies by region. BCG is routinely given to infants in most endemic countries primarily for tuberculosis protection. Boosting BCG in adolescence may extend leprosy protection.

Single-dose rifampicin (SDR-PEP) is WHO-recommended chemoprophylaxis for household and close contacts of newly diagnosed cases. A single 600 mg dose (weight-adjusted in children) reduces contact leprosy incidence by approximately 60% over 2 years.

Mycobacterium leprae grows preferentially at 30-33°C, well below body core temperature. It therefore localizes in the cooler skin, peripheral nerves, eyes, upper airway, and testes. The face, hands, and feet — typically a few degrees cooler than the core — are the most commonly affected sites.

Vertical transmission is rare. Most children born to mothers with leprosy are healthy, especially when the mother is on MDT during pregnancy. MDT (rifampicin, clofazimine, dapsone) is considered safe in pregnancy.

Clofazimine, a component of MDT, accumulates in skin and causes reddish-brown pigmentation, particularly in lesional skin. This is harmless and reversible — the pigmentation fades over 6-12 months after completing treatment.

Relapse after completed MDT is rare — under 1% over 10 years in WHO surveillance. Nerve function should be monitored every 6 months for at least 2 years after treatment because delayed reactions can occur. Any new skin lesion, sensory change, or nerve thickening should be reported promptly.

Biblical 'leprosy' (Hebrew tzaraat, Greek lepra) referred to a range of skin conditions, most of which were not actual Hansen disease. Modern Hansen disease is a specific bacterial infection identified by Gerhard Hansen in 1873.

MDT is provided free of charge by WHO worldwide through national leprosy programs. In the US, the National Hansen's Disease Program treats patients without cost regardless of insurance status.