It sounds like "soft bloat", which I do not believe is fatal (if treated) or contagious. Look more up on it, then you can be certain and try to find a vet that deals with amphibians. Even if they don't, it's a fairly simple procedure, where you drain them with a syringe. Hell, I've even heard of some brave souls who just do it themselves with some insulin needles!

You could also try to set up a little hospital tank with a little bit of aquarium salts and see if that does anything while you search around for a vet.

Also this talks a bit about soft bloat. It may go away with the salt bath!
Xenopus Disease

Information is your friend!