From Sanctuary Shard
Shapeshifters come in many forms in these land and some of them are human. Those who are "moon called" are considered Lycanthropes by most scholars of Meissa. Lycanthropes are always "bitten not born", which means they contract lycanthropy only after birth. The two most common strains of lycanthropy are wolf and cat.
Origins of this curse?, transformation?, effect? are guesses at best. The popular theory is that wolf and bear lycanthropy was transmitted to humans during fights with shape-changed Alfar and cat-based lycanthropy came in the same manner from the Children of the Forest. There are certainly more strains of lycanthropy then these three, and their origins are equally mirky.
The transformation itself is relatively straight forward. The exchange only happens when another were, in beast or beast-man form, badly savages another human. A simple bite will not suffice. The victim must be hurt nearly to the point of death to activate the curse which by activation will effectively heal the human. Its manner of activation has been proposed as being a survival trait of the pure-book Aelfeyn races.
Most lycanthropes only have a beast form, though some do develop the ability to shift parts of their body such as claws. The beast form is generally larger, heavier, and stronger than their natural counterpart.