Leprosy
Leprosy, also known as Hansen’s disease, is a chronic infectious disease that primarily affects the skin, peripheral nerves, mucosa of the upper respiratory tract, and eyes. Caused by the bacterium Mycobacterium leprae, it is one of the oldest recorded diseases in human history and carries a significant social stigma, largely due to disfigurement and disability associated with advanced cases.
Although curable, leprosy remains a public health concern in several developing nations, especially among economically disadvantaged communities. Early diagnosis and prompt treatment are critical to prevent nerve damage, deformities, and transmission.
2. Definition
Leprosy is defined as a chronic granulomatous disease caused by Mycobacterium leprae, characterized by the progressive involvement of skin and peripheral nerves, leading to hypopigmented patches, sensory loss, muscle weakness, and deformities. The disease has a slow incubation period, sometimes spanning years, making early detection challenging.
Unlike common bacterial infections, leprosy does not spread easily from person to person, and most people (approximately 95%) have natural immunity against it.
3. Epidemiology
3.1 Global Burden
According to the World Health Organization (WHO), more than 200,000 new cases of leprosy are reported annually worldwide. The highest burden is reported from countries like India, Brazil, and Indonesia, which collectively account for over 80% of global cases.
3.2 Endemic Regions
• South-East Asia: Especially India, Nepal, Bangladesh.
• Africa: Democratic Republic of Congo, Ethiopia, and Nigeria.
• South America: Brazil remains a significant contributor to new cases.
• Western Pacific and Eastern Mediterranean: Moderate incidence.
3.3 At-Risk Populations
• People living in overcrowded and impoverished settings.
• Individuals with close and prolonged contact with untreated leprosy cases.
• Children and immunocompromised individuals, though rare.
3.4 Elimination Efforts
WHO launched the Global Leprosy Strategy 2021–2030 with the theme: “Zero leprosy”, aiming for no child diagnosed with leprosy and visible deformities by 2030. India declared elimination as a public health problem in 2005 (less than 1 case per 10,000), but pockets of high endemicity still exist.
Pathophysiology of Leprosy
Step 1: Entry of the Bacteria
Leprosy is caused by Mycobacterium leprae. The bacteria usually enter the body through the nose or broken skin. They are very slow-growing and prefer cooler areas of the body, such as the skin, nose, and peripheral nerves.
Step 2: Multiplication in the Body
After entry, the bacteria multiply very slowly in the skin and peripheral nerves. Because they grow best at lower temperatures, they mainly affect the hands, feet, face, and ear lobes rather than deeper organs.
Step 3: Immune Response Determines Disease Type
The body’s immune reaction decides how severe the disease will be:
- If the cell-mediated immunity (T-cell response) is strong → the disease is limited and mild (tuberculoid leprosy).
- If the immune response is weak → the bacteria multiply freely, causing widespread infection (lepromatous leprosy).
Step 4: Nerve Involvement
Mycobacterium leprae has a special tendency to attack the Schwann cells of peripheral nerves. Infection and inflammation damage these nerves. This leads to loss of sensation (numbness) in hands and feet. Because patients cannot feel pain, burns, cuts, and injuries occur easily.
Step 5: Skin and Organ Changes
As the disease progresses, the skin shows patches, nodules, or thickened areas due to bacterial growth and immune reaction. In severe cases, the bacteria spread to the eyes, nose, and testes, causing blindness, nasal deformities, or infertility.
Step 6: Deformities and Disability
Repeated injuries due to loss of sensation, along with nerve paralysis, cause muscle weakness, ulcers, and deformities in fingers, toes, and face. These are the most disabling features of leprosy if untreated.
4. Etiology
4.1 Causative Agent
Leprosy is caused by Mycobacterium leprae, an acid-fast, rod-shaped bacillus.
• Discovered in 1873 by G.H. Armauer Hansen, making it the first bacterium identified as a cause of human disease.
• It has a very slow replication rate (doubling time ~14 days).
• M. leprae cannot be cultured in artificial media; it is grown experimentally in armadillos or the footpads of mice.
4.2 Transmission
• Transmitted primarily via prolonged close contact through nasal droplets or skin contact.
• Exact mechanism of transmission remains unclear.
• Contrary to common belief, it is not highly contagious.
• Zoonotic transmission from armadillos is reported in the southern United States.
5. Pathogenesis
Once in the host, M. leprae invades Schwann cells of peripheral nerves and macrophages in the skin, leading to nerve damage and cutaneous lesions.
• The clinical manifestation depends on the host’s immune response:
- Strong cell-mediated immunity (CMI) leads to tuberculoid leprosy (paucibacillary form).
- Poor CMI results in lepromatous leprosy (multibacillary form).
The disease spectrum represents a host-pathogen interaction, ranging from localized lesions to widespread disseminated disease.
6. Types of Leprosy (Ridley-Jopling Classification)
The clinical classification of leprosy is based on immune response, clinical presentation, and bacteriological index. WHO simplifies it into paucibacillary (PB) and multibacillary (MB) leprosy for treatment purposes.
6.1 Indeterminate Leprosy
• Earliest stage; ill-defined hypopigmented macule.
• May progress to other forms or resolve spontaneously.
6.2 Tuberculoid Leprosy (TT)
• Few well-defined hypopigmented patches with sensory loss.
• Asymmetric nerve involvement.
• Positive CMI; low bacterial load.
• Usually paucibacillary.
6.3 Borderline Tuberculoid (BT)
• More lesions than TT, slightly less defined borders.
• Asymmetric nerve thickening.
• Intermediate immune response.
6.4 Mid-Borderline (BB)
• Numerous and irregular lesions.
• Unstable immune response.
• Rare; transitional state.
6.5 Borderline Lepromatous (BL)
• Multiple lesions, often symmetrical.
• Loss of eyebrows (madarosis).
• Nerve involvement becomes more pronounced.
6.6 Lepromatous Leprosy (LL)
• Most severe form.
• Numerous nodular or infiltrative lesions.
• Diffuse thickening of skin, nasal congestion, leonine facies.
• High bacterial load.
• Symmetrical nerve involvement.
• Associated with eye, testicular, and nasal complications.
7. Clinical Features
7.1 Skin Manifestations
• Hypopigmented or erythematous patches.
• Loss of sensation (especially temperature and light touch).
• Nodules, plaques, and thickened dermis.
• Dryness and hair loss in affected areas.
7.2 Nerve Involvement
• Peripheral nerve thickening (ulnar, peroneal, facial).
• Muscle weakness, claw hand, foot drop.
• Loss of sweating and thermoregulation.
7.3 Ocular Complications
• Lagophthalmos, keratitis, iritis.
• Risk of blindness if untreated.
7.4 Nasal Involvement
• Chronic nasal stuffiness, crusting, and perforation of the nasal septum.
7.5 Systemic Complications
• Testicular atrophy, gynecomastia.
• Lepromatous leprosy may involve reticuloendothelial system.
8. Reactions in Leprosy
8.1 Type 1 (Reversal Reaction)
• Occurs in borderline forms.
• Acute inflammation in lesions and nerves due to enhanced immune response.
8.2 Type 2 Reaction (Erythema Nodosum Leprosum – ENL)
• Seen in lepromatous and borderline lepromatous types.
• Painful red nodules, fever, joint pain.
• Immune complex-mediated.
9. Diagnosis
9.1 Clinical Diagnosis
• Presence of at least one of the following:
- Skin lesion with loss of sensation.
- Thickened peripheral nerves.
- Positive skin smear.
9.2 Laboratory Tests
• Skin smears and biopsies (Ziehl-Neelsen staining for acid-fast bacilli).
• Histopathology: Shows granulomatous infiltration.
• Lepromin test: Used for classification, not diagnosis.
• PCR: Detects M. leprae DNA with high sensitivity (not routinely used).
10. Treatment
10.1 WHO Multidrug Therapy (MDT)
Introduced in the 1980s, MDT is the cornerstone of leprosy control.
Paucibacillary (PB) Leprosy:
• Duration: 6 months
• Drugs:
- Rifampicin 600 mg once monthly (supervised)
- Dapsone 100 mg daily (self-administered)
Multibacillary (MB) Leprosy:
• Duration: 12 months
• Drugs:
- Rifampicin 600 mg once monthly (supervised)
- Clofazimine 300 mg once monthly and 50 mg daily
- Dapsone 100 mg daily
10.2 Management of Reactions
• Type 1: Corticosteroids (e.g., prednisolone).
• ENL: Thalidomide (where approved), steroids, and analgesics.
10.3 Supportive Care
• Physiotherapy for muscle weakness.
• Occupational therapy.
• Reconstructive surgery.
• Psychosocial support to overcome stigma.
11. Prevention and Control
11.1 Early Diagnosis and Treatment
Interrupts transmission and prevents complications.
11.2 Contact Tracing
Close contacts should be examined periodically for signs of leprosy.
11.3 Chemoprophylaxis
• Single-dose rifampicin (SDR) for contacts reduces risk by 50–60%.
11.4 Vaccination
• BCG vaccine offers partial protection.
• Ongoing research on M. leprae-specific vaccines (e.g., LepVax).
12. Social and Psychological Aspects
Leprosy is not only a medical condition but also a sociocultural issue. Myths, fear of contagion, and historical isolation have led to widespread discrimination.
• Stigma and ostracism continue despite curability.
• Integration into society and rehabilitation programs are vital.
• Community education plays a crucial role in breaking myths.
Conclusion
Leprosy, though ancient, is still a relevant and neglected tropical disease that demands continued attention. The bacterium Mycobacterium leprae causes chronic infection of the skin and nerves, resulting in severe deformities and disability if left untreated. The disease has largely been eliminated as a public health problem in many parts of the world, yet new cases persist, especially among marginalized populations.
A multifaceted approach involving early detection, WHO-recommended MDT, management of complications, contact prophylaxis, public health campaigns, and rehabilitation can ensure sustainable elimination of this stigmatized disease. Global collaboration and community awareness are essential to move towards a leprosy-free world.
