They should have done a skin scraping the first time you brought him in. Didn't they do that? Looks like they didn't or it wouldn't have gotten this bad=poor baby.
“It came to me that every time I lose a dog they take a piece of my heart with them. And every new dog who comes into my life gifts me with a piece of their heart. If I live long enough,all the components of my heart will be dog,and I will become as generous and loving as they are"
"We never really own a dog as much as they own us!"