structural:scholar_edition, linguistic:paraphrasing
Transmission

Transmission of leprosy occurs during close contact with those who are infected. Transmission of leprosy is through the upper respiratory tract. Older research suggested the skin as the main route of transmission, but research has increasingly favored the respiratory route. Transmission occurs through inhalation of bacilli present in upper airway secretion.

Leprosy is not sexually transmitted and is not spread through pregnancy to the unborn child. The majority (95%) of people who are exposed to M. leprae do not develop leprosy; casual contact such as shaking hands and sitting next to someone with leprosy does not lead to transmission. People are considered non-infectious 72 hours after starting appropriate multi-drug therapy.

Two exit routes of M. leprae from the human body often described are the skin and the nasal mucosa, although their relative importance is not clear. Lepromatous cases show large numbers of organisms deep in the dermis, but whether they reach the skin surface in sufficient numbers is doubtful.

Leprosy may also be transmitted to humans by armadillos, although the mechanism is not fully understood.