In this article we will discuss about Mycobacterium Leprae which causes Leprosy:- 1. Morphology of Mycobacterium Leprae 2. Cultivation of Mycobacterium Leprae 3. Antigenic Structure 4. Clinical Features 5. Ridley and Jopling’s Classification 6. Difference between Lepromatous Leprosy and Tuberculoid Leprosy 7. Complications of Therapy and Other Details.
Contents:
- Morphology of Mycobacterium Leprae
- Cultivation of Mycobacterium Leprae
- Antigenic Structure of Mycobacterium Leprae
- Clinical Features of Mycobacterium Leprae
- Ridley and Jopling’s Classification of Mycobacterium Leprae
- Difference between Lepromatous Leprosy and Tuberculoid Leprosy
- Complications of Therapy
- Immune Reaction
- Lepromin Test
- Significance of Lepromin Test
- Laboratory Diagnosis
- Treatment
1. Morphology of Mycobacterium Leprae:
M. leprae occur singly in parallel bundles (like cigarettes in a packet). They are slender, slightly curved or straight rods, measuring 1-8 µm x 0.2-0.5 µm, with considerable variation in size. The fragmented, granular bacteria are seen in smears from skin, mucous membrane scrapings of nasal septum of patients under treatment.
Though they are Gram-positive, they cannot be easily stained by Gram stain as they contain wax like substance (mycolic acid) in their cell wall; but they can be stained by Z-N method by substituting 5% sulphuric acid (H2SO4) for 20% which is used for decolourisation after staining with steamed carbol fuchsin.
They are uniformly stained solid rods in smears from patients without treatment in endothelial cells of bl
ood vessels or in mononuclear cells.
2. Cultivation of Mycobacterium Leprae:
M. leprae cannot be grown on artificial media and tissue culture which are still under controversy. Their generation time in experimental animals is about 12-13 days.
They can be cultivated in experimental animals:
(1) Mouse
(2) Armadillo,
(3) Monkey of West Africa or chimpanzee which were found to suffer from natural disease (Leprosy).
The relationship of this natural disease with human infection is yet to be established.
3. Antigenic Structure of Mycobacterium Leprae:
M. leprae contain carbohydrate and a characteristic surface lipid, phenolic glyco lipid I (PGL I). This lipid has been extracted from M. leprae and a carbohydrate antigenic determinant has also been synthesised from its carbohydrate and used to prepare a monoclonal antibody.
This antibody can be used to detect and identify M. leprae in tissues. Besides, they also contain a unique O-diphenoloxidase, an enzyme characteristic of Lepra bacilli from armadillo or human tissue.
Resistance:
Lepra bacilli can survive in ultraviolet light for 30 minutes, in warm humid environment for 9-16 days, and in moist soil for 96 days.
Pathogenesis Clinical Features:
Leprosy is a chronic progressive disease of man. Lepra bacilli prefer lower temperature, therefore they localize in superficial cooler tissue, i.e. skin, ears, nasal mucosa and peripheral nerves, lungs, liver, testes, eyes and bones are also affected.
The incubation period is 3-15 years. Nasal discharge and skin lesion are the sources of infection. Lepra bacilli enter through damaged skin, cut, wound and nasal mucosa. The transmission of the disease is mostly by prolonged contact with infective patients.
Schwann nerve cell is the target for these bacilli; thereby the nerve is damaged and ultimate manifestations of Leprosy are anesthesia and muscle paralysis. Visible lesions are due to infiltration of M. leprae into skin and cutaneous nerve. The first sign of Leprosy that heals spontaneously is a non-specific or inflammatory or indeterminate skin lesion.
4. Clinical Features of Mycobacterium Leprae:
Clinically there are four types of Leprosy:
(1) Lepromatous or nodular type;
(2) Tuberculoid type;
(3) Dimorphous or borderline type;
(4) Indeterminate type.
Delayed type hypersensitivity plays a great role in determining the response of the host to infection and production of clinical type: Tuberculoid type of Leprosy is very common in patients with high degree of Cell-Mediated Immunity (CMI); whereas in lepromatous type leprosy the cell-mediated type immunity is either absent on deficient.
The indeterminate form occupies a position between the two extreme forms (tuberculoid and lepromatous type). According to alteration of immune status of the host and chemotherapy clinical type of Leprosy may change.
(1) Lepromatous or Nodular Type:
It is a generalized form of Leprosy and is encountered in individuals where the host resistance is low. The course of the disease is progressive and severe with nodular skin lesions (lepromata) on face, ear lobes, hands, feet and trunk.
There is slow thickening of peripheral nerves and anesthesia. Large number of M. leprae present in skin lesions and in mucosa of nose, mouth and upper respiratory tract are shed in sweat, nasal and oral secretions.
The granulation tissue with a large aggregation of vacuolated mononuclear cells containing lepra bacilli is a characteristic feature of lepromatous to repeated trauma and may get secondary infected resulting to distortion and mutilation of extremities.
Lepromatous leprosy is more infectious than other types. It is severe and its prognosis is poor due to deficient MI (Table) humoral antibodies against mycobacterial antigens are not protective. Lepromatous leprosy patients give false positive reaction in standard serological tests for syphilis.
(2) Tuberculoid Type:
It is a localised form of the disease and found in patients with high degree of CMI and the skin is infiltrated with helper T-cells. The course of the disease is benign, non-progressive and is self-healing. The skin lesions are few and consist of non-elevated hypo- or hyper- pigmented macular anaesthetic patches on the face, trunks, and limbs.
The deformities of hands and feet are due to thickened, hard, tender nerve trunks. Lepromin test is positive due to high degree of CMI. Anti-mycobacterial and autoimmune antibodies are rarely produced.
(3) Dimorphous or Borderline Type:
In this type, the lesions clinically resemble tuberculoid leprosy, but bacteriologically and immunologically resemble lepromatous type. Depending on chemotherapy and alterations in resistance of the host, this clinical form may shift to any of the two extreme types.
(4) Indeterminate Type:
In this type, there is a mild transient tissue lesion, resembling maculo-anaesthetic patches, due to an early unstable tissue reaction. This is either characteristic of tuberculoid nor lepromatous type. Skin scraping for M. leprae examination and lepromin test are either negative or positive. The lesion heals spontaneously in many persons and in others it may progress to tuberculoid or lepromatous type.
5. Ridley and Jopling’s Classification:
For therapeutic purpose, they classified Leprosy into 5 groups:
(a) Tuberculoid;
(b) Borderline tuberculoid;
(c) Mid-borderline;
(d) Borderline lepromatous;
(e) Lepromatous.
According to World Health Organisation (WHO), Leprosy is divided into two groups: Paucibacillary which includes all tuberculoid types and multi-bacillary which includes all lepromatous types and some borderline type.
6. Difference between Lepromatous Leprosy and Tuberculoid Leprosy:
7. Complications of Therapy:
I. Lepromatous Type:
There may be suddenly acute exacerbation, testicular atrophy, necrosis of bone and cartilage, loss of upper incisor teeth, diffuse thickening of the face.
II. Tuberculoid Type:
Peripheral neuropathy may occur due to delayed hypersensitivity reaction to degenerated lepra bacilli. Corneal ulcer may occur due to damage of Vth and Vllth cranial nerves, foot drop in lateral popliteal nerve damage; loss of digits due to absorption of phalanges from base or due to osteomyelitis resulting from trauma to the insensitive area followed by secondary bacterial infection.
8. Immune Reaction:
Immune reactions in leprosy cause additional tissue damage. They are due to delayed hypersensitivity reaction (Jopling type I reactions) or to formation of antigen antibody complexes (Jopling type 2 reactions, erythema nodosum).
Jopling type I reaction is observed in borderline cases which may lead to permanent nerve damage while Jopling type 2 reaction in borderline lepromatous and lepromatous leprosy (Table 41.1).
9. Immunity:
A high degree of innate immunity exists in man for this disease, but only few contacts develop clinical diseases. The infection induces both humoral and cell mediated immunity; the circulating antibodies have no effect but the cell mediated immunity plays an important role for the response of the host for this infection.
Tuberculoid type develops in patients with hypersensitivity. Lepromatous type may develop in those with deficient cell mediated immunity.
10. Lepromin Test:
Lepromin is a boiled (sterilised) extract of Lepromatous tissue in isotonic saline. When 0.1 ml of lepromin (containing 40 millions dead lepra bacilli) is injected intradermally to an individual, it produces at the site of injection an area of nodular infiltration in skin which reaches its maximum size in 3 to 5 weeks. The lepromin test can detect the hypersensitivity in a leper.
There are two types of reactions:
(1) Early reaction,
(2) Delayed reaction.
There is also another type of skin testing reagent known as Leprosins which are ultrasonates of tissue-free bacilli from lesion. They are designated as Leprosin H if it is from human origin and Leprosin A if from Armadillo origin. Type of reaction elicited by Leprosins is similar to that of Lepromin:
1. Early or Fernandez Reaction:
Erythema and induration of 10-30 mm in diameter is observed after 24-48 hours after injection.
2. Delayed Mitsuda Reaction:
Similar nodular lesion of 3-5 mm in diameter appears in 3 to 5 weeks after injection. This test is negative in lepromatous leprosy and is positive in tuberculoid leprosy. The positive reaction is an indication of resistance to leprosy.
11. Significance of Lepromin Test:
1. Classification of Leprosy:
On the basis of Lepromin test, Leprosy can be classified into:
(a) Lepromatous leprosy, if this test is negative;
(b) Tuerculoid type, if it is positive;
(c) Borderline and indeterminate leprosy, if lepromin test is either negative or weakly positive.
2. Prognosis of Leprosy: If the test is positive, the prognosis is better, if negative reaction converts into positive during treatment, it shows an improvement by therapy.
3. Assessment of resistance to leprosy is preferable for field workers. They should be lepromin positive.
12. Laboratory Diagnosis:
A. Direct Skin smear Examination:
Smear made from the scraping of skin, ear lobes, patches, nodules etc. can be stained by modified Z-N method using 5% sulphuric acid and examined. The living bacilli stain uniformly as a strong rod; whereas dead bacilli are fragment and granular.
Demonstration of bacilli under microscope is a direct evidence of Leprosy:
1. Bacteriological Index:
It is associated from stained smear by oil immersion lens (x 100) of microscope. International bacteriological index is from 1 to 6+:
1-10 bacilli in 100 fields = 1 +
1-10 bacilli in 10 fields = 2 +
1-10 bacilli per field = 3 +
10-100 bacilli per field = 4 +
100-1,000 bacilli per field = 5 +
More than 1,000 bacilli per field = 6 +
2. Morphological Index:
It is the percentage of uniformly stained bacilli in a lesion out of the total bacteria present in the lesion and it can assess the prognosis and response of the disease to the drug.
B. Histological Examination of Skin Nerve Biopsy:
When lepra bacilli cannot be demonstrated by direct smear the histological examination of the biopsy material can be undertaken to confirm tuberculoid leprosy.
C. Animal Inoculation:
Injection of ground tissue from the lesion into foot pad of mouse may produce typical granuloma in six months. This test is also useful to confirm doubtful diagnosis, to test drug resistance and to evaluate antimicrobial activity of newer drugs.
D. Indirect Method:
1. Lepromin Test:
Though it is useful to assess the prognosis of leprosy, it has a limited diagnostic value.
2. Serological Test:
Various serological tests were aimed at the detection of anti-phenolic glycolipid I (anti-PGL I) antibodies. They are latex agglutination, Mycobacterium leprae Particle Agglutination (MLPA) test and ELISA. In MLPA test, gelatin particles coated with natural.
Trisaccharide phenyl propionate Bovine serum Albumen (NTPBSA) has a stable hydrophilic substance that exhibits stronger sero reactivity than the natural PGL I antigen used to detect anti-PGL I antibodies. Anti-PGL- I antibody titres are very high in new untreated lepromatous cases as compared to old treated patients.
The Tuberculoid cases show low titres.
The positivity rate is as follows:
Lepromatous (78-80%); borderline (45-50%) and tuberculoid (20-22%). The antibody titres decrease following effective chemotherapy. Standard Serological Test (STS) gives false positive reaction in lepromatous leprosy.
13. Treatment:
Dapsone (4.4′ diamino diphenyl sulphone) (DDS) mono-therapy was standard drug for all types of Leprosy till 1982. Later WHO recommended multi-drug therapy (MDT) for all types of Leprosy by the use of rimfapicin, dapsone and clofazimine (Table 41.3).
Epidemiology:
Man is the main source of infection. Nasal secretions and discharges from nodular lesions are infectious materials for family contacts by inhalation and through the skin. Transmission of Leprosy occurs in children exposed to heavy shedders of bacilli for long period.
Blood of lepromatous leprosy patients may have adequate number of bacilli which may be transmitted by blood-sucking insects. Leprosy is endemic and widespread in the underdeveloped countries—mainly Asia and Africa. Out of 11 million world-wide cases, four million are in India.
Prevention and Control:
BCG vaccine seems to give some protection against leprosy in children of 0-15 years in countries where BCG vaccine was used against tuberculosis. Similar trial in children in Myanmar (Burma) claimed 82% protection where lepromatous leprosy is prevented.
Recent vaccine (LEPROVAC) stimulates immune system to kill M. leprae and accelerates bacterial clearance which enables the patient to be cured under experimentation.