what is the pathway or process of mycobacterium leprae into the body to cause leprosy?

Answer 1

Mycobacterium leprae enter body via skin ( close contact ). But it has a very low transmisibility and hence it is only after a prolonged contact ( over months )with a leprosy patient that you might get the disease.

Answer 2

Note the factual and neutrality warnings on the wiki article..Still a good article.