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Mycobacterum Leprae

  1. Acid fast with 5% H2SO4.
  2. Masses of 50 or more organisms known as globi are seen inside histiocytes which have a foamy appearance –Virchow’s lepra cells
  3. Morphological index : % of uniformally stained bacilli (used for prognosis)
  4. Bacteriological index: Total no. of acid fast bacilli in an oil immersion field
  5. Generation time-8-32 days. Not cultivable on cell free media
  6. Recently a new Mycobacterium causing disseminated leprosy has been characterized-M. lepromatosis 

A. Experimental animals used for culture

  1. Monkeys: Rhesus, African green, Cynomolgous
  2. Chimpanzees, Gibbon apes, Hamsters, Lewis rats
  3. Mice (foot pad, most common animal used)
  4. Armadillo (best animal model)
  5. Slender loris, Indian pangolin 

B. Antigenic structure

M leprae : Group I & IV

  1. Group I common to all mycobacteria
  2. Group II slowly growing species
  3. Group III rapidly growing species
  4. Group IV Unique to each species 

C. Important Points

  1. LAM - B : External to cell wall dominant antigen serodiagnosis
  2. PGL-I outermost layer protects against host cell enzymes, suppresses CMI
  D. Characteristics of 5 forms of leprosy
 
 

 

TT

BT

BB

BL

LL

AFB in the skin

-

+/-

+

+++

++++

AFB in nasal secretions

-

-

-

+

++++

Granuloma formation

++++

+++

+

-

-

Lepromin reaction

++++

+

+/-

-

-

Antibodies to M. leprae

+/-

+/-

+

+++

++++

 

E. Reactions inLeprosy

  1. Type I reversal reaction-
    1. Occurs in BB, BT, BL due to development of CMI
    2. Lesions infiltrated with lymphocytes and epitheloid cells with reduction in no. of bacilli
  2. Type II, Erythema nodosum leprosum (ENL) –
    1. Seen in LL undergoing chemotherapy
    2. Lesions show intense neutrophilic infiltration 

F. Diagnosis

  1. Nasal scrapings (positive in patients who are infectious), Slit skin smear from skin lesions, punch    biopsy of skin
  2. Bacteria disappear more rapidly from nose as a result of chemotherapy





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