Mycobacterium Leprae - Treatment, Immunology, Transmission, Lepra Reactions

Treatment of Mycobacterium leprae

Mycobacterium leprae infection can be treated by the use of drugs:

• Single skin lesion => rifampicin (600 mg), ofloxacin (400 mg), monocycline (100 mg) – single dose

• Paucibacilliary disease => dapsone (100 mg), rifampicin (600 mg) – once a month for 6 months

• Multibacillary disease => rifampicin (600 mg – once a month), dapsone (100 mg – daily), clofazimine (300 mg – once a month), clofazimine (5 mg – daily for 1 year)

Immunology of Mycobacterium leprae

The immunology of Mycobacterium leprae depends upon:

Tuberculoid leprosy

• Patients produce a cell-mediated response to M. leprae

• Skin tests with lepromin elicit a strong positive response

• tuberculoid leprosy also has a TH1- type response producing interleukin – 2 and interferons – γ

• These strong cell-mediated responses clear Ag but cause local tissue destruction

Lepromatous leprosy

• Patients in this cast do not produce a normal CMI

• Patients are also unresponsive to lepromin

• Lepromatous leprosy has specific T-cell failure and macrophage dysfunction and problems producing IL-2 and IL-γ

• But they do not produce TH2- type cytokines

Transmission of Mycobacterium leprae

In the 19th century, leprosy caused by Mycobacterium leprae, was believed to be hereditary. The main reservoir is humans and the transmission occurs through the respiratory tract although the exact mechanism is not known.

Risk groups include children, people living in endemic areas, in poor conditions, with insufficient diet, or having a disease that compromises their immunity (i.e. HIV).

Lepra reactions by Mycobacterium leprae

They are those reactions stage during the course of leprosy, which occurs in 1/3rd of the patients. They are of allergic nature so there is actual inflammation. These reactions are considered a medical emergency, requiring immediate treatment and management.

Lepra reactions caused by Mycobacterium leprae include:

• Lepra type I (reversal) reaction

• Lepra type II reaction or erythema nodosum leprosum (ENL)

• Lucio phenomenon

Lepra type I (reversal) reaction

• Lepra type I (reversal) reaction is a type IV cell-mediated hypersensitivity

• This reaction is mostly seen in patients with borderline leprosy, occurring spontaneously more often during chemotherapy

• These reversal reactions, caused by Mycobacterium leprae, usually suggest a shift toward tuberculoid form after the start of chemotherapy

• The reaction usually occurs during the first 2 months of therapy to up to 12 months

• These reactions are characterized by the development of skin erythema with edema and tenderness of peripheral nerves

Lepra type II reaction

• Lepra type II reactions are type III humoral hypersensitivity reactions with a systemic inflammatory response due to the deposition of immune complexes

• This condition occurs in 20% of patients with lepromatous leprosy and 10% of patients with borderline leprosy

• This reaction occurs after a few years of therapy and relapses intermittently over several years

• The appearance of painful erythematous nodules on the skin and subcutaneous tissue is the characteristic manifestation of Mycobacterium leprae infection

• Fever, malaise, arthralgia, neuralgia, arthritis, and protein urea are other symptoms

Lucio phenomenon

• Lucio phenomenon is an unusual form of type II reaction

• This concentration manifests as cutaneous hemorrhagic infarct in patients with diffuse lepromatous leprosy

• This concentration of Mycobacterium leprae infection is commonly documented in Mexico and Central America