MYCOBACTERIUM LEPRAE
It is a causative agent of leprosy.
MORPHOLOGY:-
Shape:- it is a slender
slightly curved or straight Bacilli.
Size:- 1.8 um × 0.2-0.5
um .
Nature:- Acid-fast Bacilli
and gram-positive Bacilli.
Staining:- It stains more
readily with the help of the Ziehl - Nelson method, the live Bacilli stain
uniformly and appear solid and the dead Bacilli are fragmented and granular.
Appearance:- Inside the cell, they are present in parallel rows gives an appearance of the CIGAR BUNDLE.
ANTIGENIC STRUCTURE:-
The wall of the M Leprae
is made up of 4 layers -
a. Peptidoglycan
layer.
b. Lipoarabinomanan-B.
c. Mycolic
acid.
d. Mycosides.
RESISTANCE:-
Lepra Bacilli can survive-
- In the warm humid environment for 9 to 16 days.
- In moist soil for 46 days .
- On exposure to the UV for 30 min
- To direct sunlight for 2 hrs.
PATHOGENESIS:-
Leprosy
is a chronic granulomatous disease of the human.
Source of Infection:- Patient
Only. Nasal discharge, skin lesions, and prolonged close contact with the patient
are necessary for transmission.
Location:- The Bacilli
primary localize in the skin and peripheral nerves and nasal mucosa but any
tissue or organ may be involved.
Incubation period:- very
long and variable.
TYPES OF LEPROSY:-
1. Lepromatous type:-
- It is a generalized form of the disease and found in individuals with low resistance. This form is severe and more infectious and the prognosis is poor.
- This test is negative due to the deficiency of CMI (cell-mediated immunity). Autoantibodies are produced.
Sign and Symptoms:
- Nodular skin lesions (lepromata) on the face, ear lobes, hands feet.
- Slow and segmental thickening of peripheral nerves.
- Due to the loss of sensation the skin lesion accurately with reacted trauma
- The ulcerated nodules becomes secondarily infected, leads to distortion and mutilation of extremities.
2. Tuberculoid type:-
- This is a localized form of disease and occur in patient having a high degree of resistance.
- Lepromin test is positive due to intact CMI.
Sign and Symptoms:
- Skin lesions are few and consist of non-elevated hypo or hyperpigmented macular patches involving face , limbs, and trunk .
- It involves local peripheral nerves which gradually extend to larger nerves and trunks which become hard , thicker and thickened.
- Deformities of the limb.
3. Dimorphic Type:-
- In this type the lesions clinically resemble tuberculoid Leprosy but the bacteriological and Immunological picture is that of lepromatous type.
- It may be shift between the two types.
4. Indeterminate type:-
- There is an early unstable tissue reaction with mild transparent tissue lesion often resembling macules anesthetic patches.
- The lesion heals spontaneously or may progress to tuberculoid or lepromatous type.
The immune reaction in Leprosy are of two types:-
A) Type-
I (Reversal Reaction):- It is due to delayed hypersensitivity reaction or may
lead to permanent nerve damage.
B) Type
– II (Erythrema Nodosum leprosum):- It is seen in the lepromatous Leprosy patient undergoing
chemotherapy. It is due to the formation of the antigen-antibody complex.
LEPROMIN TEST:-
The reaction is first described by Mitsuda in 1919.
The original antigen (lepromin)
was boiled, emulsified, lepromatous tissue rich Lepra Bacilli.
The lepromin used as a
antigen are of two types -
a. Integral Lepromin:- Mitsuda’s
crude antigen is called the integral antigen which is prepared from armadillo-derived
M. leprae.
b. Bacilliary Lepromin:-
It is prepared by floating out bacilli from finely ground lepromatous tissue
with chloroform evaporating it dry and removing the lipid by washing with
ether.
Procedure:-
It is carried out by the
intradermal injection of 0.1 ml of Lepromin.
Result:-
The response is typically
biphasic consisting of-
a. Early reaction of
Fernandez:- It consists of erythema and induration developing 24-48 hrs and
usually remains for 3-5 days.
b. The late reaction of Mitsuda:-
It appears 1-2 weeks after the infection, reaching to peak in four weeks. The
reaction appears in the form of a nodule that may ulcerative. It indicates the resistance of Leprosy.
Uses:-
- Classification of Leprosy:- Tuberculoid and Lepromatous.
- Assessment of progenesis.
- Assessment of the Resistance:- It is Indicate by a positive Lepromin test.
LAB DIAGNOSIS:-
- Specimens :- collected from nasal mucosa, skin lesions, and ear lobules.
- Serological test- It carried out by the detection of anti-phenolic glycolipid-1 antibodies.
- Acid-fast staining.
- Skin and Nerve Biopsy.
- Lepromin test.