Leprosy is a chronic bacterial disease and it is caused by Mycobacterium leprae. Leprosy was first observed by Hansen in 1868 so also known as Hansen disease. It mainly affects the skin, eyes, nose and peripheral nerves.
It is a gram-positive acid-fast bacteria for which 5% percent sulphuric acid is used for the decolorization after staining with carbolfuchsin.
Antigenic structure
Inner most cell wall of bacteria is made of peptidoglycan. External to this is the lipoarabinomanan-B (LAM-B) layer, attached to mycolic acid. Outermost layer is composed of mycosodes which is composed of phenolic glycolipids-1 (PGL-1).
LAM-1 is highly immunogenic and is used in the serodiagnosis of leprosy.
Pathogenesis
- Source of infection is patient in case of Leprosy.
- Source of infection are nasal discharge and skin lesion of patient.
Types of Leprosy
- A. Based on CMI
- B. Based on clinical pathological and immunological findings
- C. Based on the number of lesions and involvement of nerve trunks (WHO)
A. Based on CMI:
The type of leprosy in an individual is determined by the status of cell-mediated immunity. Infection with mycobacterium leprae produces both humoral and cell-mediated immunity. Patients with deficient cell-mediated immunity develop the lepromatous type of disease and when cell-mediated immunity is adequate, the lesions are of tuberculoid type.
There are 4 type of leprosy
1. Lepromatous Leprosy
2. Tuberculoid Leprosy
3. Dimorphous Leprosy
4. Indeterminate Leprosy
Lepromatous and tuberculoid type of leprosy are two extreme forms of leprosy.
| Features | Lepromatous leprosy | Tuberculoid leprosy |
|---|---|---|
| Form of disease | Generalized form | Localized form |
| M. leprae in lesions | Numerous/many | Scanty/little |
| Infectivity | Highly infectious most infectious | Usually Non-infectious |
| Cell-Mediated Immunity | Deficient/absent | Adequate |
| Lepromin test | Negative | Positive |
| lesions | Nodular skin lesions know as Lepromata | hypo or hyperpigmented macular patches |
| Antibodies | Abundant | Rarely produced |
| Resistance | Low | High |
B. Based on clinical pathological and immunological findings
On the basis of clinical pathological and immunological findings, Ridley & Jopling’s classifying leprosy into five groups.
- Tuberculoid (TT)
- Borderline tuberculoid (BT)
- Borderline (BB)
- Borderline lepromatous (BL) and
- Lepromatous (LL)
| Character | Tuberculoid (TT) | Borderline-Tiberculoid (BT) | Borderline (BB) | Borderline Lepromatous (BL) | Lepromatous (LL) |
|---|---|---|---|---|---|
| Lepromin test | +++ | + | +/- | – | – |
| Antibodies to M. laprae | +/- | +/- | + | ++ | +++ |
| Bacilli in skin | – | +/- | + | ++ | +++ |
| Bacilli in nasal secretion | – | – | – | + | +++ |
| Granuloma formation | +++ | ++ | + | – | – |
C. According to WHO, type of leprosy
Leprosy is classified into two classes, This classification is based on the number of skin lesions & involvement of the nerve.
a. Paucibacillary Leprosy
b. Multibacillary Leprosy
| Leprosy | number of skin lesion | Involvement of nerve |
|---|---|---|
| Paucibacillary | five or less than five | no or one nerve trunk |
| Muiltibacillary | Six or more than six | more than one nerve trunk |
Immune reactions in leprosy may cause additional tissue damage. These are two types
- Type 1 (reversal reaction type)
- Type 2 (Erythema nodosum leprosum, ENL)
| Type 1 (reversal reaction type) | Type 2 (Erythema nodosum leprosum, ENL) |
|---|---|
| Occurs in Borderline Leprosy | Occurs in Lepromatous leprosy taking treatment of Leprosy |
| Due to Delay type Hypersensitivity (CMI) | Due to the formation of Ag:Ab reaction |
| may lead to permanent nerve damage | Red nodules appear in the skin |
Epidemiology of leprosy
Source of infection of Mycobacterium leprae is the patient. nasal secretions and discharges from superficial lesions are the most likely infectious materials. The mood of entry may be either through the respiratory tract or to the skin.
The incubation period is very long and averages two to five years it may vary up to 30 year.
Lepromin test
it is not a diagnostic test but it is used to access the resistance of a person to Mycobacterium leprae infection. This reaction was first described by Mitsuda in 1919. He was used lepromin as Antigen.
Nowadays, two types of lepromins antigens are used:
- Lepromin-H (Human origin)
- Lepromin- A (Armadillo derived)
A lepromin test is carried out by the intradermal injection of 0.1 ml of lepromin.
Read more Lepromin Test click here
Laboratory diagnosis of Leprosy
1. Specimens
3. Skin and nerve biopsy
4. Animal inoculation
5. Serological test
Prevention of leprosy
- Early early diagnosis and treatment
- Surveillance surveillance of contacts
- Health health education
- Vaccination
There are no effective vaccine against leprosy but a number of vaccines have been tried.
Following list of various candidate vaccine trade
- BCG vaccine
- Armadillo derived killed M.laprae
- Combination of BCG & KILLED M.leprae
- ICRC bacillus
- Mycobacterium ‘w’
Treatment of LEPROSY
Pharmacological treatment of Leprosy: Click here
Leprosy: Important key points
- Mycobacterium leprae produces leprosy in human and only source of infection is patient.
- Lepromin test is delayed type of hypersensitivity reaction. This test can be used to classify leprosy assessment of prognosis and assess the resistance of a individual to leprosy.
- Laboratory diagnosis of electricity depends on demonstration of bacilli in specimen by microscopy.
- The specimen sample from skin erupted by slit and scrap method.
- Bacteriological index is defined as number of Total bacilli in a tissue.
- Morphological index is defined as the percentage of live bacilli out of the total number of bacilli.
- Mycobacterium leprae has not yet been given on artificial culture media for tissue culture.