Lycanthropy

is a 'disease' that turns people into werewolves.

The Saga of Darren Shan
Lycanthropy is only mentioned slightly in The Saga by the mention of the Wolf Man.

The Wolf Man
The Wolf Man is a permanent werewolf meaning that he may or may not suffer from lycanthropy. He is the only mentioned werewolf in the book series so it is unknown if he does suffer from lycanthropy or if he is just a hairy, aggressive, wolf-like human.

The Demonata series
Lycanthropy is a major part of The Demonata series and plays a big part in the build up to the last book.

History
Between 350AD and 400AD, Bec McConn's actual family were suffering as their numbers were dwindling. They needed to find a way to get their numbers up and that is when the Demonata came into their world. The Demonata bred with the humans and they had babies. Some would transform into a wolfen-like creature in their teens. These were the first Werewolves. They were chained up in a few houses to stop them from killing any one. The lycanthropy gene was passed on through people and so the 'curse' was born.

Known Lycanthropy Sufferers
People known to have suffered from Lycanthropy are:
 * Grubbs Grady
 * Gret Grady
 * Bill-E
 * Curly
 * Larry
 * Moe