It is caused by Mycobacterium leprae affects the skin & peripheral nerves. The causative organism is less acid-fast than tubercle bacillus.

MORPHOLOGICAL FEATURES:-

Grossly–

These are characterized by the development of nodules or masses formed in the skin, particularly on the face, hands & feet.

-It is a slow communicable disease & the incubation period between first exposure & appearance of a sign varies from 2-20 years. The infectivity from direct contact patient, who shed numerous bacilli from damaged skin or nasal secretions or maybe through the maternal-fetal transmission.

Microscopically-

In the dermis, there is a proliferation of macrophages with foamy changes, particularly around blood vessels, nerves, these are called lepra cells.

– Lepra cells are heavily laden with acid-fast bacilli staining, seen as globular masses, arranged in parallel fashion like “cigarette in a pack”.

– This dermal infiltrate of lepra cells characteristically does not encroach upon the basal layer of epidermis & separated from the epidermis by an uninvolved area- “clear-zone”.

– The epidermis overlying the lesion is thinned out, flat or even ulcerate.