Most likely the poor pup has autoimmune problems, like others have said. If a daily eye was kept open for things that pop up, it wouldn't be such a big deal, usually. I have two autoimmune weimaraners, its heritary. If the adult dog or grump has an autoimmune disease, it should never be bred because you end up w/pups that suffer their entire lives from one thing or another. My two are "only" hypothyroid" and get a tab twice a day. One of them also has seasonal allergies that I treat with a daily spoon of honey, ingested. Most of my dogs are allergic to corn, one of the fist three or four ingredients listed in most dog/puppy kibbles.
Saving this pup and ensuring it never had puppys or impregnanted another dog would be very rewarding, it only takes heart and determination- four hundred dollars is nothing compared to a life. If a veterinarian would take payments and someone was willing to spend the time to do the baths and give their heart, responsibly.
I always ask myself: What if that poor soul was me? What if that suffering soul was a child? That always has the same answer- Just do it! Why has someone waited this long? Because others have turned a blind eye...our rescue person is not the first person to see how this pup has suffered. Others have turned their backs and shielded their eyes, repulsed, instead of lending a helping hand.
One of the very first reasons I liked this group is because so many members have a caring heart and also knowledge in working w/animals, knowledge of health issues and they "Just do it" when something lands in their lap- they don't waste time but do the right thing...