I did not understood it correctly, perhaps because of my bad English.
Does your dog have symptoms of demodex?
Are your symptoms all gone, only biting is still?
Had your doctor made a test, or he has only prescribed drugs.
Unfortunately I cant help you, I have also something like this. could be, perhaps a new kind of mites.
in this article, you can read about 5 unidentified mites. http://www.cabdirect.org/cabdirect/abstract/19910505562