Leprosy is caused by a bacterium, Mycobacterium leprae, which is
closely related to the organism causing tuberculosis. The
mechanism of infection is not fully understood, but it is
generally thought to be by droplet spread through the upper
respiratory tract. The incubation period is long, usually
between 2 and 8 years, but it can be up to 20 years in some
cases.  Casual contact with a person affected by leprosy does
not seem to lead to infection. The evidence suggests that
residence for several years in an endemic area is needed before
the risk of infection becomes appreciable. The current strategy
to control leprosy involves early case finding and treatment
with antibiotics, with the aim of stopping transmission of the
disease to new contacts.  WHO gives an overview of leprosy and
leprosy control activities around the world. ILEP Member
Associations support leprosy activities on a country-by-country
basis throughout the world. In the USA, the Center for Disease
Control (CDC) , gives general information abou