Morphology, laboratory diagnosis of Mycobacterium leprae

Morphology
Cultivation
Leprosy
Resistance
Clinical types
Lab diagnosis
Treatment
Pathogenesis

2. Mycobacterium
leprae

3. Morphology:
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The acid-fast bacilli are arranged singly, in parallel bundles
(like rolls of cigarettes in a packet) or in globular masses.
The bacilli are slender, slightly curved or straight rods, 1-8
um X 0.2-0.5 um in size.
They are Gram positive and acid fast but to lesser extant than
tubercle. bacilli.
They are aerobic rod shaped.

4. Cultivation:
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Mycobacterium leprae is found only in cases of human
infection.
leprae bacilli like grow Intracellularly ,typically within skin
histocytes and endothelial cells and Schwann cells of the
peripheral nervous.
They have not been grown on artificial media or tissue
culture
The generation time of Leprae bacillus from animal
experiments is found to be 12 to 13 days on the average but
me very from 8 to 42 days compared to about 14 hours in
cases of turbercle bacillus and about 15 minutes in case of
E.coli.
it was first discovered by shepard 1960 that lepra bacilli
f

5. Mouse:
●When ground tissue or nasal scrapping from of a patient of
lepromatous leprosy containing lepra bacilli are inoculated
(inoculum of 100 -1000 organisms) intradermally into foot pad
of mouse and kept at a low temperature (20 °c) ,a
granulomatous lesion develops at the site of infection 1 to 6
months time with limited multiplication of bacilli, replications
reaches up to ceiling of 10
6
organisms.

6. Armadillo:
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The nine-banded armadillo (Dasypus novemcinctus) is.
highly susceptible to leprosy
When an armadillo is inoculated with lepra bacilli, it develops
genera- lised infection with extensive multiplication of the bacilli
and the lesions produced resemble lepromatous leprosy.
Natural infection by a mycobacterium resembling lepra bacillus
has been observed in some wild caught armadillos in Texas and
Mexico.
The wild armadillo, therefore, should be screened for
mycobacterial infection and kept in quarantine for 3 months
before inoculation.
The yield of lepra bacilli from armadillo skin leproma is 100 to
1000 times more than that of human lepro- matous nodule.
However, only about 40% of animals are sus- ceptible to
disseminated form of leprosy.

7. Leprosy:
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A chronic granulomatous disease prin involving Skin,
Peripheral nerves, mucosa Nasal
Incubation period 3-15 years.
Source of infection- nasal discharge & skin lesions.
Portal of entry- inhalation of infectious aerosols, through
skin contact (damaged skin) and prolonged close contact
with infective paitents. Principle target cell- schwann cell,
resulting in nerve damage causing manifestations of leprosy
(anesthesia and muscle paralysis).

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Resistance:

Viable for 9-16 days in warm humid environment.

In moist soil for 46 days

Direct sunlight for two hours.

Ultraviolet light for 30 minutes.

9. Clinical types:
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Lepromatous or nodular type
Tuberculoidtype
Borderline type
Indeterminate type
Lepromatous or nodular type:
It is a generalised form of the disease and found in
individuals where the host resistance is low. The course is
progressive and severe with nodular skin lesions (lepromata)
on face, ear lobes, hands, feet and, less commonly, trunk.

10. Tuberculoid type:
This is a localised form form of the diseases and found in
patients with high degree of resistance where cell
mediated immunity is intact . On microscopic examination
the skin is infiltrated with helper T-cells Langhan’s gaint
cells ,epithelioid cells and feelw or on acid -fastbacilli.

11. Dimorphous or borderline type:
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Borderline leprosy is a cutaneous skin condition with numerous skin lesions that
are red irregularly shaped plaques.
In this type lesions produced possess characteristics of both lepromatous and
tuberculoid lesions.
This lesions clinically resembles lesions of tuberculoid leprosy but
bacteriologically resembles lesion of lepromatous type.
Indeterminate type:
In this type, the lesions produced
often resemble

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maculo-anesthetic patches which are neither characteristic of
lepromatous or tuberculoid type.
In some cases these lesions heal spontaneously while in others it
may progress to lepromatous or tuberculoid type.
Laboratory Diagnosis:
1. Specimens
Nasal smear

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Skin smear
Slit skin smear
Nerve biopsy
2. MICROSCOPY
Diagnosis consists of demonstration of acid fast bacilli in
the lesions.
Smears are stained by Z.N (Ziehl-Neelsen) staining
technique.
5% sulphuric acid is used as decoloriser.

14. Bacteriological index(BI)
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This is an expression of the extent of bacterial loads.
It is calculated by counting six to eight stained smears
under the 100 x oil immersion lens.
Indicates the Prognosis of the Disease.
Total score in all smears / Number of smears
Eg 16/8 =2
So the index is 2
The Morphological index (MI)

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This is calculated by counting the numbers of solid-staining acid-
fast rods. Only the solid- staining bacilli are viable.
3. Culture
Mouse foot pad
Armadillo
4. Serology
Detection of antibody against M.leprae phenolic glycolipid
antigen is a specific diagnostic test.

16. Treatment of leprosy:
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Multidrug regime
Paucibacillary lesions:-
Rifampicin 600 mg / once month
Dapsone 100 mg/day for 6 months
Multibacillary lesions:-
Rifampicin 600 mg / once month
Dapsone 100 mg/day
Clofazimine 50 mg daily
D Continue for two years.

17. Pathogenesis
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Chronic granulomatous disease
Patient is the only source of infection-nasal
discharge&skin lesion
Mostly affects the cooler parts of the body skin, eyes
and nasal mucosa.
Incubation period- long&variable

18. Pathogenesis
Entry of Mycobacterium leprae inside Host Body
Binds with the Schwann cell of PNS
Immune response through Cytokines by APS
Initiation for Phagocytosis
Which eventually leads to damage of Schwann cell

19. Thank you