Quote Originally Posted by spyder View Post
It's caused by bacteria, so any way that you can get sick from bacteria, you can get leprosy.
This article is a bit over my head, but it does suggest there's some gray area. Of course, I'm just a computer nerd, so what I think I know about most things is just unverifiable crap found on the interwebs.

The ancient disease of leprosy can cause severe disability and disfigurement and is still a major health concern in many parts of the world. Only a subset of those individuals exposed to the pathogen will go on to develop clinical disease and there is a broad clinical spectrum amongst leprosy sufferers. The outcome of infection is in part due to host genes that influence control of the initial infection and the host's immune response to that infection. Identification of the host genes that influence host susceptibility/resistance will enable a greater understanding of disease pathogenesis. In turn, this should facilitate development of more effective therapeutics and vaccines. So far at least a dozen genes have been implicated in leprosy susceptibility and a genome-wide linkage study has lead to the identification of at least one positional candidate. These findings are reviewed here.