Well, if there were diseases, at least the Potion of Vitality would have some real use. I don't think Larian would implement Exhaustion, which is one of its primary functions beside boosting hp gain when using Hit Dice. Larian doesn't seem to want to challenge the player, challenge would likely be considered 'not fun' by their target audience. I mean, it's not like there's a 2nd level spell, copious scrolls, and even an amulet that would remove disease just like that.
