Leprosy, also known as Hansen’s disease, is a chronic infectious disease caused by slow-growing bacteria Mycobacterium leprae or M. lepromatosis. It mainly affects the skin, peripheral nerves, mucous membranes, eyes, hands, feet and testicles. Leprosy is a slowly progressing disease — symptoms may appear anytime from 6 months to 40 years after infection.
Humans are the main source of infection, but rare transmission occurs from animals like armadillos, chimpanzees and mangabey monkeys. The disease forms granulomas (inflammatory nodules) in skin and nerves, similar to tuberculosis.
Historical note: Leprosy is one of the oldest diseases known to mankind. Mycobacterium leprae was discovered in 1873 by G.H. Armauer Hansen — the first bacterium proven to cause a human disease.
Classification of Leprosy
Leprosy is broadly grouped into three clinical types:
1. Paucibacillary (PB) / Tuberculoid Leprosy
- 1 or few light or dark skin patches with loss of sensation
- Peripheral nerves may be swollen
- Commonly affected nerves include great auricular, ulnar, median, radial, peroneal, tibial and sural nerves
- Strong immune response keeps bacteria limited
2. Multibacillary (MB) / Lepromatous Leprosy
- Widespread skin lesions without clear loss of sensation
- Multiple nodules, plaques and thickened dermis
- High bacterial load; numerous acid-fast bacilli in tissue
- Involves eyes, nose, testes and bones in advanced stages
- Nasal congestion and nosebleeds are common
3. Borderline (Dimorphous) Leprosy
- Most common form
- Features of both tuberculoid and lepromatous leprosy
- Multiple skin patches with nerve involvement and sensory loss
Pathogenesis of Leprosy
Leprosy begins slowly and mainly affects nerves, skin and eyes. It may also involve the mouth, nose, muscles, kidneys and blood vessels.
- Bacteria usually enter via the respiratory tract.
- Only a small percentage of infected individuals develop the disease due to naturally strong immunity.
- Bacteria migrate to nerve tissues and enter Schwann cells.
- They multiply very slowly (division time ~12–14 days).
- Once bacterial load increases, the immune system reacts, causing inflammation.
The outcome depends on the patient’s cell-mediated immunity (CMI):
- Strong immunity → PB leprosy
- Weak immunity → MB leprosy
- Sudden immune changes (e.g., during treatment) can cause Type 1 or Type 2 leprosy reactions.
Signs and Symptoms
Skin Symptoms
- Light or dark skin patches with numbness
- Skin nodules and lumps
- Thick, dry skin
- Painless ulcers on feet
- Loss of eyebrows or eyelashes
- Facial swelling or lumps
Nerve-Related Symptoms
- Numbness or loss of sensation
- Muscle weakness or paralysis of hands/feet
- Thickened peripheral nerves (commonly near elbow, knee or neck)
- Eye problems leading to blindness if facial nerves are affected
Mucosal Symptoms
- Stuffy or blocked nose
- Nosebleeds
Advanced Untreated Leprosy Can Cause:
- Claw-like deformities of hands and feet
- Shortening or absorption of fingers and toes
- Chronic foot ulcers
- Blindness
- Nasal collapse and facial deformity
- Painful, tender nerves
- Burning sensation in affected skin areas
Diagnosis
Diagnosis is mainly clinical in most settings.
- Skin patches with sensation loss + thickened nerves strongly suggest leprosy.
- Skin smears or biopsies show acid-fast bacilli in MB leprosy.
- If bacilli are absent → PB leprosy.
- Advanced tests like PCR, lepromin test or PGL-1 test are used only in specialized centres.
- Additional tests (CBC, LFT, creatinine, nerve biopsy) help check organ involvement.
Treatment
The WHO recommends Multidrug Therapy (MDT). Early treatment stops progression and prevents disability.
Standard MDT Regimens
1. Paucibacillary (PB) Leprosy
- Dapsone
- Rifampicin
- Duration: 6–12 months
2. Multibacillary (MB) Leprosy
- Dapsone
- Rifampicin
- Clofazimine
- Duration: 12 months or more
New WHO recommendation: A single-dose regimen (rifampicin + minocycline + ofloxacin) may be effective for patients with only one skin lesion.
Supportive Treatments
- Steroids for painful leprosy reactions
- Eye care and artificial tears
- Physiotherapy for nerve damage
- Management of ulcers and deformities
Complications
Without treatment, leprosy can cause permanent damage.
- Blindness or glaucoma
- Facial disfigurement
- Kidney damage
- Erectile dysfunction and infertility (in men)
- Permanent nerve damage in arms, legs and feet
- Claw hand and foot drop
- Chronic nasal congestion and nose deformity
Prevention
- Early diagnosis and MDT treatment to stop transmission
- Public education to reduce social stigma
- Regular screening of household contacts
- Single-dose rifampicin prophylaxis for high-risk contacts
- BCG vaccine provides partial protection
- No fully protective vaccine exists yet
Detailed Notes:
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