Leprosy is a contagious disease. It has been known for a very long time. Today, it is mostly called Hansen's disease, named after the person who discovered the bacterium, Gerhard Armauer Hansen. It is caused by a bacterium, Mycobacterium leprae. A person with leprosy is called a leper.
As of 2004, the estimated number of new infections was about 400,000.
Getting the disease is hard, since it requires close contact with someone who has it, over a long period of time. In addition, about 95% of people seem to be naturally immune to it.
Most cases of leprosy occur in India, and other developing countries. It has known to have been in the US before. There are practically no cases of leprosy in the developed world. This is because there are excellent drugs and people regularly take antibiotics which will kill the leprosy bacteria.
In former times, leprosy was seen as a divine punishment for sins committed.