Swamp Fever World Change/Spoiler

Find Ottokar in Venore's poor house here. Go out the south-west exit and walk east below the bridge then north along the path.

He will inform you about his fight against Swamp Fever. Only the poorest of Venore get the disease, but the cure is not hard to obtain. Feverish Citizens may appear throughout Venore and may attack you - they suffer from Swamp Fever (spawn time varies from 30 minutes to 1 hour and more depanding on the amount of Medicine Pouchs given to Ottokar). If you kill them, only to protect yourself, they may drop certain pieces of cloth needed for the Afflicted Outfits Quest.

In order to prevent the fever from spreading a certain number of medicine bags must be given to Ottokar each day. You can go south of Venore to the Swamp Troll Cave and hunt them for these medicine bags. You could also go to the Port Hope Swamp Trolls. In exchange for medicine bags, he will give you the Belongings of a deceased patients. These bags may contain a number of things including Slug Drug which can be used to tame wild slugs.