Mycobacterium leprae causes leprosy, also known as Hansen's Disease. It is an acid-fast rod that cannot be grown in artificial media and grows best at low temperatures. Leprosy damages the skin, superficial nerves, eyes, nose, and testes. There are 5 subdivisions based on the level of cellular immunity, ranging from Lepromatous leprosy which has very low immunity and involvement of multiple areas, to Tuberculoid leprosy which has intact immunity and self-limiting localized involvement. The different classifications represent a spectrum between these two polar forms.

1. Microbiology:Chapter 14
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Mycobacterium leprae

2. 01
Acid-fast rod
Impossible to grow on artificial media
• (Grown in the foot pads of mice,
armadillos, and monkeys)
Nonmotile
Facultative intracellular growth

3. Metabolism 02
Catalase-positive
Grows best at low temperature
Phenolase-positive

4. 03
Mycobacterium leprae causes leprosy,
also called Hansen's Disease.

5. 04
- Infection occurs when a person is exposed
to the respiratory secretions or skin lesions
of an infected individual.
- Cell-mediated immunity (cellular immunity)
limits the spread of the bacteria. However,
it causes inflammation and granulomas.

6. 05
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Leprosy damages
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the skin (sparing
warm areas such as
the armpit, groin,
and perineum), the
superficial nerves,
eyes, nose, and
testes

7. 5 Subdivisions based on the level
of cellular immunity 06
• Lepromatous leprosy (LL)
Tuberculoid leprosy (TL)
Borderline lepromatous (BL)
Borderline (BB)
Borderline tuberculoid (BT)

8. Lepromatous leprosy (LL)
Severest form of leprosy
- Patients with LL cannot mount a
delayed hypersensitivity reaction.
- Very low cellular immunity
Involves skin, nerves, eyes, and testes
Acid-fast bacilli are found everywhere
LL will lead to death if untreated

9. Tuberculoid leprosy (TL)
Milder and self-limiting disease
- Patients with TL can mount a cell-
mediated defense
- Delayed hypersensitivity reaction
is intact.
- Patients demonstrate localized
superficial, unilateral skin and nerve
involvement; non-infectious and
spontaneously recover.
Bacilli are difficult to find in lesions or
blood

10. BL, BB, and BT 09
Borderline lepromatous (BL). Borderline
(BB), and Borderline Tuberculoid (BT)
Represent a continuum between LL
and TL
** The skin lesions of BL will be more
numerous and have a greater diversity
of shape than those of BT

11. Spcectrum of Leprosy
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Tuberculoid
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Borderline Lepromatous
Number of skin lesions
Single Several Many
Hair growth on skin lesions
Absent Slightly decreased Not affected
sation in lesions of the extremities lost
Completely Moderately lost Not affected
Acid-fast bacilli in skin
None Several Innumerable
scraping
Lepromin skin Strongly positive No reaction No reaction
test