by doing the main quest, you get Sainies Lupinus (werewolf disease). After you get it, if you want to keep doing the main quests, you have to cure it (back to the fort shrine or cure common disease potion). There are some really cool missions ahead so i would recomend this.
You get a mission where you have to do a load of mazes, and the fight some powerful beast. You get a ring when you are near *a man* (u will see who), that lets you turn into a werewolf. Don't use it near people, or u will get hated forever (like me

)
Hope this helps
beware of shifty people