Instructions
Travel to the northwest corner of the main Morrowind island until you reach a small fishing village.
Speak with the lady standing in front of a large boat with a sail, who will give you the option to travel to Solstheim island.
Travel from the main landing on Solstheim into the northern portions of the island and wait until nightfall.
Roam around the northern portion of the island during the night hours and you will eventually encounter a werewolf during a randomly generated combat event. This can take two or three nights to occur, so use patience when waiting.
Engage in combat with the werewolf until you receive a notification that you have contracted Sanies Lupinus.
Travel to a safe location on Solstheim and wait for a full 72 hours (three days) without using any healing potions or seeking medical attention from a doctor. After three days with no medical attention, you will become a werewolf and will transform into the werewolf form at night.