I emailed a friend whose relative just went through mange with their dog and this is what he said:
in the month Feb.-March each year I give Dixie a pill obtained from ProHeart(online).Each pill contains 136 micrograms of MOXIDECTIN which is a specific for heartworm,hookworm,roundworm,whipworm ,fleas and sarcoptic mange.
He forgot to do it this year and poor dog Dixie got mange. Worse was that the young vets didn't have a clue what they were looking at. Fortunately, an older vet came along and immediately diagnosed it - after the family had already spent a lot of money on incorrect prescriptions. Hope you have better luck.