Also known as Hansen's disease, leprosy has been known to humankind for millenia.
The causative organism was not found until 1873, when a Dr. Gerhard A. Hansen (1841-1912) discovered that leprosy was caused by Mycobacterium leprae. Since then, leprosy has also been known as Hansen's disease (personally, I'm pretty sure I wouldn't like to be remembered as the guy whose name is associated with leprosy ...).
Mycobacterium leprae is an obligate intracellular parasite that is from the same family of acid-fast bacili that causes tuberculosis. This particular bug has never been grown on any sort of artificial medium. Humans were the only known natural reservoir for Mycobacterium leprae until recently when some armadillos in Louisiana and Texas were found to be infected. Armadillos also seem to be a good culture animal for leprosy for some reason, as Mycobacterium leprae creates an even bigger infection in armadillos than in humans.
Most cases of leprosy occur in Africa and Asia. Other endemic foci exist in Central and South America. In the U.S. and Europe, leprosy is almost unknown outside of immigrants from these areas.
Transmission of leprosy is uncertain. Leprosy was even thought to be a hereditary disease (a long time ago), as there did not seem to be any pattern for the transmission of this disease. Close contact is certainly necessary for transmission of leprosy and it is thought that Mycobacterium leprae is spread via the respiratory tract. Few who actually come into close contact with a leper end up getting leprosy but many will end up developing antibodies to Mycobacterium leprae.
The incubation period for leprosy can range from one year to 40 years, with an average of 5 to 7 years. Mycobacterium leprae grows very slowly, with a doubling time of about two weeks.
hmm... more later.
One thing that piqued my interest in an article on leprosy in the November 2000 edition of Discover magazine was that leprosy was brought back to Europe in large numbers by warriors returning from the Crusades. The church had trouble answering why these fighters were coming back diseased when they had gone on a holy war (as in "whose side was God on?") - leper colonies only became prominent after the Crusades. Leprosy in Europe died out when the Black Death a.k.a. the Plague came along and wiped out most of the lepers (along with a quarter of Europe's population).