We still do not have a simple field based serological test to identify susceptible people who are at risk of developing leprosy (specially people with “anergy” who are likely to show infectious form of disease).

Tests such Lepromin (like Montaux in TB), PGL-1, PCR are not sensitive and specific enough to meet the requirements of a public health strategy.

Disease transmission from healthy carriers – not understood.

http://bphc.hrsa.gov/nhdp/FAQS_MAIN_PAGE.htm