Mycobacterium leprae and Leprosy

Mycobacterium leprae (Leprosy)

• Leprosy is a chronic infectious disease caused by Mycobacterium leprae, an acid-fast, rod-shaped bacillus.
• Primarily affects the skin, peripheral nerves, and mucosa of the upper respiratory tract, and also the eyes, excluding some other structures.
• Human-only disease; no animal reservoir.

Transmission

• Transmission occurs through infectious droplets spread via coughing and sneezing.
• Some individuals can carry the disease without developing symptoms (healthy carriers).

Pathogenesis

• Incubation period is prolonged, averaging 5 years, ranging from 3 to 30 years.
• Only a portion of infected individuals develop the disease (5-10%).
• M. leprae targets Schwann cells, which protect peripheral nerves.
• Infection leads to bacterial replication within the cells and an immune response, causing skin and nerve inflammation.
• Nerve damage is the main clinical characteristic, leading to anaesthesia and muscle paralysis.
• Repeated injury to affected areas contributes to gradual nerve destruction.
• Bacilli infiltration of the skin and cutaneous nerves results in visible lesions, often with pigment changes.

Initial Signs

• Initial symptoms are nonspecific skin lesions that often heal spontaneously
• This is followed by characteristic skin lesions

Skin Lesions

• Variations in lesion appearance exist, including loss of sensation alongside visual signs of damage.

Types of Leprosy

• Hyper-reactive tuberculoid (TT) leprosy: Characterized by a small number of localized skin lesions. Few bacilli are present, making them undetectable via microscopy. The immune response is intense and damages nerves.
• Anergic lepromatous (LL) leprosy: Numerous or confluent skin lesions contain high numbers of bacilli, often visible as clusters. Cooler body parts, such as earlobes, are heavily affected; no evidence of an immune response.

Clinical Manifestations

• Disease progression depends greatly on the patient's immune response to the bacteria.
• Distinct differences in immunological responses lead to different clinical outcomes.

Complications

• Nasal bone destruction can cause nasal collapse.
• Eye damage, frequently characterized by direct bacillary invasion leading to eyelid paralysis, is common.
• Blindness is a significant and unfortunate consequence of untreated leprosy.
• Continued nerve damage and other complications are possible in untreated cases. Additional tissue damage may occur due to delayed hypersensitivity or a vasculitis associated with anti-body complex formation

Diagnosis

• Diagnosis relies primarily on patient history and a thorough clinical examination for leprosy signs.
• Laboratory testing is rarely needed except in unique situations.

Suspected Leprosy Cases

• In endemic areas, an individual with at least one of various symptoms (e.g., pale or reddish, hypo-pigmented patches on the skin) should undergo appropriate examination.
• Examples of characteristic symptoms include:
  • Pale or reddish, hypo-pigmented skin patches (possibly with sensory loss)
  • Painless swelling or nodules on the face and/or earlobes
  • Enlarged and tender nerves
  • Burning sensations in the skin
  • Numbness or tingling in the hands and/or feet
  • Weakness of eyelids, hands, or feet
  • Painless wounds or sores on the hands or feet

Cardinal Signs of Leprosy Diagnosis

• A skin lesion combined with loss of sensation
• One or more enlarged peripheral nerves
• A positive skin smear

Classifying Leprosy

• Classified based on the number of skin lesions and presence of bacilli in skin smears, helping direct treatment decisions.
• Multibacillary (MB) leprosy: 6 or more skin lesions and a positive skin smear.
• Paucibacillary (PB) leprosy: 1 to 5 skin lesions and a negative skin smear.

Laboratory Diagnosis Confirmation

• Confirmation of diagnosis involves:
  • Histological examination of skin biopsies
  • Detection of acid-fast bacilli in nasal discharges or scrapings
  • Slit skin smears (made from superficial skin incisions to sample tissue fluid and cells)
  • Smears using the Ziehl-Neelsen method, and others.

Morphological Index and Drug Compliance

• The morphological index (percentage of viable bacilli) decreases during treatment.
• Its increase could indicate patient non-compliance. Additional factors, like drug resistance, are also considered.

Treatment

• Treatment utilizes multi-drug therapy (MDT) with Rifampicin, Clofazimine and Dapsone.
• Treatment duration varies depending on the type (MB or PB) and is a vital factor in successful treatment, typically ranging from 6 to 18 months for multibacillary leprosy and 6 to 9 months for paucibacillary cases.
• Avoiding single drug treatment is essential to prevent drug resistance.

Control

• Early detection and treatment are crucial.
• No vaccine is currently available.
• Health education plays a vital role in prevention and management.

This quiz explores the chronic infectious disease leprosy, caused by the bacterium Mycobacterium leprae. Discover its transmission, pathogenesis, and impact on human health, including the specific effects on the skin and nerves. Test your knowledge on one of humanity's oldest diseases.