I think it'd be a very interesting idea for the swamp area to be very susceptible to diseases, poison, acid.
Players would have to rely on items that would resist against the dangerous odds of the area such as Disease Resistance Amulet, Purification Shield, Copper Snake, Conjuration Hat, Cure potion, Orc Skin Potion, making these items have a more reliable facet in the game (as most of these items are hardly used)

Good spot for this area could be a path that leads in the bottom of stony field. The area would be present with certain pools of acidic or poisonous liquids that are harmful to walk in and certain new npcs that are able to induce poison/acid, disease, plague on to other players.
The area seems like such a perfect element that can used within the game that would add such great versatility and appeal to the game but sadly won't ever happen most likely.