Oh no! Distemper is nasty

. Is he staying at the vet hospital or is he at home now? If he's at home, make sure to keep him hydrated. That's a big threat with Distemper. Otherwise all you can do is wait for it to run its course, and hope he doesn't end up with lasting neurological damage. I wish him luck!
Have you called his breeder? He/she should know, in case the other pups were exposed.