Some people who are exposed to Mycobacterium leprae develop a single, self-healing skin lesion. But in others, the infection
can develop into a noninfectious (paucibacillary) form, involving few lesions
with no detectable M leprae, or an infectious form,
featuring numerous lesions with readily detectable levels of the pathogen.
Contributing to these varied outcomes, researchers believe, are genetic differences
in those exposed to the bacteria that determine their vulnerability to infection
and how the disease is manifested.
Stephenson J. Genetic Susceptibility to Leprosy Infection. JAMA. 2003;289(10):1234. doi:10.1001/jama.289.10.1234-a