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 about leprosy. The Report of the ILA Technical Forum (394KB), held in Paris in 2002, reviews much of the scientific evidence underpinning current efforts to control leprosy.