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.