Introduction
- Leprosy, also called Hansen’s disease, is a chronic infectious disease caused by Mycobacterium leprae.
- The disease primarily affects the skin, peripheral nerves, mucosa of the upper respiratory tract, and eyes.
- It is a slowly progressive bacterial infection because Mycobacterium leprae multiplies very slowly inside the human body.
- The incubation period is prolonged, usually 3–5 years, but in some cases symptoms may appear only after 10 years or more.
- Early manifestations commonly include hypopigmented skin patches, loss of sensation, and thickening of peripheral nerves.
- If not diagnosed early, leprosy can lead to nerve damage, muscle weakness, deformities, and permanent disability.
- Historically, leprosy carried severe social stigma, but today it is a completely curable disease with early diagnosis and proper treatment.
- World Health Organization recommends multidrug therapy (MDT), which has greatly reduced disease burden worldwide.
- India remains one of the countries where new cases are still reported, making leprosy an important public health concern.
- Effective public health programs, contact screening, and early treatment are essential to prevent transmission and disability.
Causative Organism
- It cannot be cultured on artificial laboratory media.
- It grows extremely slowly.
- It prefers cooler body temperatures, which explains why lesions commonly appear on:
- face
- ears
- hands
- feet
- peripheral nerves
Another species, Mycobacterium lepromatosis, has also been identified in some leprosy cases.
Important Characteristics of Mycobacterium leprae
- Acid-fast organism
- Intracellular pathogen
- Affinity for Schwann cells of peripheral nerves
- Very long generation time (approximately 12–14 days)
Mode of Transmission
Leprosy spreads mainly through prolonged close contact with untreated infected individuals.
Main routes of transmission:
- Nasal droplets from infected patients
- Respiratory secretions
- Prolonged household exposure
It is important to understand that leprosy is not highly contagious. Casual contact such as:
- shaking hands
- sharing food
- sitting nearby
usually does not transmit infection.
Risk factors include:
- Poor immunity
- Malnutrition
- Overcrowding
- Long-term exposure to untreated patients
Pathogenesis
After entering the body, Mycobacterium leprae targets:
- Skin macrophages
- Peripheral nerves
The organism especially invades Schwann cells, causing:
- nerve inflammation
- demyelination
- sensory loss
The type of disease that develops depends mainly on the host immune response.
Strong cell-mediated immunity leads to:
- localized disease
- few lesions
- tuberculoid form
Weak cell-mediated immunity leads to:
- widespread disease
- multiple lesions
- lepromatous form
Thus, immunity determines clinical severity.
Classification of Leprosy
The most widely used classification is based on the Ridley–Jopling spectrum.
This form occurs in patients with strong immunity.
Features:
- Few well-defined hypopigmented patches
- Marked sensory loss
- Nerve thickening
- Dry skin
- Hair loss over lesions
Bacterial load:
Very low.
Smear:
Usually negative.
2. Borderline Leprosy
This is immunologically unstable and may shift toward either pole.
Features:
- Multiple lesions
- Irregular margins
- Partial sensory loss
- More nerve involvement
3. Lepromatous Leprosy (LL)
Occurs in patients with poor immunity.
Features:
- Numerous symmetrical lesions
- Nodules
- diffuse infiltration
- loss of eyebrows
- thickened skin
Classical facial appearance:
Leonine facies
Bacterial load:
Very high.
Smear:
Strongly positive.
WHO Operational Classification
For treatment purposes, World Health Organization classifies leprosy into:
Paucibacillary (PB)
- 1 to 5 skin lesions
- smear negative
Multibacillary (MB)
- More than 5 lesions
- smear positive or clinically extensive disease
Clinical Features
Skin Manifestations
The earliest sign is usually a hypopigmented or erythematous patch with sensory loss.
Common skin findings:
- Pale patches
- Dry lesions
- Hair loss
- Reduced sweating
- Nodules
- plaques
- diffuse infiltration
Nerve Involvement
Peripheral nerve damage is the hallmark of leprosy.
Commonly affected nerves:
- ulnar nerve
- common peroneal nerve
- posterior tibial nerve
- facial nerve
Symptoms:
- numbness
- tingling
- muscle weakness
- claw hand
- foot drop
Eye Involvement
Untreated disease may affect eyes and cause blindness.
Ocular manifestations:
- lagophthalmos
- keratitis
- corneal ulcer
- iridocyclitis
Nasal Involvement
Particularly common in lepromatous leprosy.
Features:
- nasal stuffiness
- epistaxis
- septal damage
Lepra Reactions
Leprosy patients may develop acute inflammatory episodes called lepra reactions.
Type 1 Reaction (Reversal Reaction)
Occurs mainly in borderline disease.
Features:
- sudden redness of lesions
- swelling
- painful nerves
- worsening sensory loss
This is due to increased cell-mediated immunity.
Type 2 Reaction (Erythema Nodosum Leprosum)
Seen mainly in lepromatous leprosy.
Features:
- painful nodules
- fever
- arthritis
- neuritis
- orchitis
This is an immune complex-mediated reaction.
Diagnosis
Clinical Diagnosis
Diagnosis is often based on three cardinal signs:
Cardinal signs:
- Skin lesion with sensory loss
- Thickened peripheral nerve
- Demonstration of acid-fast bacilli
Skin Smear Examination
- earlobes
- lesions
- elbows
Staining is done by Ziehl–Neelsen stain.
Positive smear shows:
- acid-fast bacilli inside macrophages
Skin Biopsy
Histopathology helps classify disease.
Tuberculoid leprosy shows:
- granulomas
- giant cells
- few bacilli
Lepromatous leprosy shows:
- foamy macrophages
- numerous bacilli
Lepromin Test
This test assesses immunity, not diagnosis.
Positive in:
- tuberculoid leprosy
Negative in:
- lepromatous leprosy
Treatment
World Health Organization recommends Multidrug Therapy (MDT).
Paucibacillary Treatment
Drugs:
- Rifampicin
- Dapsone
Duration:
6 months
Multibacillary Treatment
Drugs:
- Rifampicin
- Dapsone
- Clofazimine
Duration:
12 months or longer
Management of Lepra Reactions
Type 1 reaction:
- corticosteroids
Type 2 reaction:
- corticosteroids
- Thalidomide (in selected cases)
Prevention
Early Detection
Early diagnosis prevents disability.
Contact Screening
Family members of patients should be examined regularly.
Chemoprophylaxis
Single-dose rifampicin may be given to close contacts.
Vaccination
BCG vaccine offers partial protection.
Complications
Untreated leprosy can lead to severe disability.
Major complications:
- claw hand
- foot drop
- trophic ulcers
- blindness
- facial deformity