Ash is right... there's some sort of virus(?--not sure that's exactly what it is) that g.piggies can carry and, while it doesn't hurt the g.piggie, it can be fatal to the bun. I have NO IDEA if a vet can test for this virus. You might call Julian's vet and ask!

Good luck in your search -- let us know what you find out. I'll see if I can find info on it after I get off of work.