What is the time period for which mycobacterium leprae remain active on dry surfaces?

Leprosy: Most scientists believe that m. Leprae transmission is from person to person in respiratory droplets. Unfotunately over 50% of people with leprosy have no confirmed contact with an infected person. The organism has never been grown in vitro (in lab media), and doubt that anyone knows how long it can survive on inanimate objects.

Unknown: Mycobacteria including mycobacterium tuberculosis can remain active on dry surfaces for months. However, it is unknown how long mycobacteria laprae would remain active.