Lycanthropy is typically transmitted through a bite or scratch from an infected lycanthrope, making it contagious. It can also be a hereditary curse passed down through bloodlines, or a result of a dark ritual. The origin can be tailored to suit your setting and storyline.
The disease is not easy to remove as most simple diseases. Most Paladins are immune to the effect however. The DC can for removal can be challenging based on the skill roll challenge creature who bit its fortitude vs fortitude .