Demodex is defined as a loss of hair in patches that is caused by the demodex mite who becomes active when the immune system is down on a pup/dog. Most dogs have demodex mites which is acquired from nursing. They are not transmitted through the mother's milk, but from the skin and hair follicles. In most pups or dogs, the mites stay dormant through the entire life of the dog because the immune system is high. This is not a disease. It is not inherited through the genes.
In most cases that you see on YouTube, the animal has been neglected by the irresponsible dog owner. A responsible dog owner will see a small patch of hair loss, maybe in several places. The dog needs to be taken to the vet for a skin scraping to find out if it is demodex in the early stages. Home remedies are not the solution to rid of demodex. Take demodex seriously, take action immediately or it can become deadly. Keep the immune system high so the mites don't become active.
Many vets will blame the demodex on the breeder, but if you look back from generation to generation, it has been around for a long, long time. Think of where the breeder got their dogs from and where that breeder got theirs from and so on. It doesn't stop.
These mites don't care if their host is a dog in a good home or a stray off the street or a World Champion. They just wait on their host. Don't let them become active. Feed high quality food, high quality supplements and don't let your dog get stressed out either which can cause the immune system to go down.
If you look at many of the YouTube videos, you will see that this mite is all over the world. Look at the video below and the pictures so you are aware of the demodex mites.