Leprosy (Hansen’s disease) is a
chronic, systemic infectious disease,
affecting primarily the peripheral
nerves and secondarily the skin,
mucous membranes, the eyes,
bones, lymph nodes and viscera.
Chronic granulomatous infection caused by Acid
Fast Bacteria Mycobacterium leprae (Ml)
Ml cannot be grown on culture media--- in vitro
drug sensitivity is not possible
Growth and Drug susceptibility are done by
injecting inoculate in mouse foot pad
Live dormant in macrophages but alive
Transmitted from person to person through nose,
skin lesions of the infected persons.
Affect mainly PNS, NS, Skin and various tissues
Bacteria Resides in
Cooler Parts of the Body
Mode of infection:
Leprosy is slow communicable disease and
uncubation period is between first exposure
and appearance of signs of disease.
Direct contact: Prolonged close contact of
susceptible individuals to an open case of
leprosy (damaged skin, nasal secretions,
mucous membrane contact).
Materno- foetal transmission.
Transmission from milk from mother to
They act as animal
model along with
monkey, mice and
At highest risk are those living in endemic
areas (hot and moist) with poor
conditions such as inadequate bedding,
contaminated water, and insufficient diet,
or other diseases that compromise
Acc to WHO- India, Brazil, Indonesia,
Myanmar and Nigeria are with the most
Main 2 types:
Tuberculoid type: high resistance.
Lepromatous or low resistance
Cass not falling in these 2 are considered
as borderline leprosy.
Based on the clinical, bacteriologic, immunologic and
histopathologic features, leprosy is classified into main
1. Paucibacillary example: (Tuberculoid leprosy) (TL)
(with scanty or absent bacilli) - Skin lesions,
loss of sensation.
2. Multibacillary (Border line) (with numerous
bacilli)---numerous skin lesions, loss of sensation,
can go to
3. Multibacillary (lepromatous leprosy) (LL).
Nodules and plaques, thickened dermis, loss of
sensation, neuronal damage, nasal congestion,
Leprosy attacks the nervous system,
particularly the nerves of the hands, feet and
In tuberculoid leprosy, skin lesions typically
develop in areas of nerve damage. Skin
becomes pale, may develop a reddish copper
Lepromatous leprosy: Loss of sensation to pinprick or light touch. Starts at the fingers and
toes, affect a small patch of skin to begin with,
but as time passes many skin lesions and
nodules develop. Organ deformaties
The bacilli are usually absent in slit-skin
The histopathology shows tuberculoid
granulomas composed of epithelioid cells
surrounded by a zone of lymphocytes.
Lepromin test is strongly positive.
Cutaneous lesions consist of
macules, papules, infiltration or
They are numerous, bilateral,
symmetrical, ill-defined with shiny
The sites commonly affected are
the face, arms, legs and buttocks,
but may be anywhere.
2. Skin Smear Tests
Ziehl Neelsen Carbol Fuchsin Stain (ZNCF)
Absence of bacteria in smear: Paucibacillary
Presence of bacteria in smear: Multibacillary
3. Lepromin test
It is an immunologic test indicative of host resistance to
A sample of inactivated (unable to cause infection)
leprosy-causing bacteria is injected just under the skin,
usually on the forearm
Tuberculoid: The immune system recognizes and
produces allergic reaction: Positive
Lepromatous: The immune system does not recognizes
Mechanism of Nerve Damage
Entry Through Blood Vessels
Outcomes of Nerve Damage