Leprosy is caused by Mycobacterium leprae, which is an aerobic (oxygen dependant) rod shaped acid-fast bacillus that spreads through droplet infection. It has never been grown in culture media but has been grown in footpads of the nine-banded armadillos. This bacterium has a long incubation period of 5 years in man and multiplies very slowly. Children are more susceptible than adults. Man is the only source of infection. They mainly spread through droplet infection. A large number of bacteria are shed in the nasal secretions and from the superficial lesions and nasal secretions of the multibacillary type of leprosy.
Mode of entry:
respiratory tract or skin.
Asymptomatic infections are very common.