I just had some experience with demedex, The pup was in extremely poor shape when I bought it from someone other than the breeder and within a week he was loosing hair. I went to two vets and both said cut the dogs nutts and pay them a ton... I know the blood line the pup came from and trust the breeder way more than any vet after talking to him I trusted that it was not something genetic... Two months later after getting the pups immune system back up and going he has a full good looking coat with ZERO meds...Building the immune system is nothing more than making sure the dog is fed properly and is free of worms and such. I did a ton of reading on demedex and found several articles supposedly written by new age vets stating that ALL dogs have the demedex mite it is just the immune system being weak that allows the mange reaction to happen.. It went on to say that something like 85% of dogs if left alone would develop and immunity to the mite and start killing off the over population. This is the case in most Localized demedex cases the generalized demedex cases are usually the ones that are genetic and will come back if treated...I am not claiming to know it all about this just throwing my 2 cents in to the hat

I hope the best for your dog...