The shapeshifter could only be infected if their shifting was magical in nature, which would make them a mage; if it's not a magical ability, then they wouldn't be at risk for infection. As to how being around someone with the curse would affect them, that'd be up to you to decide. x3 The effects of the curse on the environment and people around it are generally chaos and madness and entropy, so if you felt having them lose control of their shifting would be good, then go for it!
The curse could only infect a magically created creature if they possessed magic of their own. :3 As for how being around someone cursed would affect them, well, same as above! That'd be up to the player to decide. x3
If they have spells on, but don't have magic of their own, it would make those spells go haywire for as long as they were in the ruins/around an infected person, but the person wearing them could not be infected unless they were a mage themselves.
Basically, if you are a mage, you can be infected. If you're not a mage but have a magic item/spell on your person, that item will go haywire while you're exposed but you can't be infected or anything. x3 Whether or not there's permanent damage to the item/spell, and what exactly those affects are, I'll leave that up to the players to decide. ^^ React however feels appropriate.
