Are you sure his teeth are good? My girlie stopped eating kibble when her slightly bad teeth caused sores on her upper gums, so if you or your vet can get a really good luck in his mouth, I would suggest that.
Jennie
Dehydration, infection, and possible temporary diabetic-like symptoms due to diet or lack thereof. A vet will be able to assess better. I have no words whatsoever for the "person" caring for this poor girlie .
Miss Jennie