Hello! My cat has had exactly the same thing for the past 3 years, we've spent a fortune on various tests & treatments, nothing which makes it go away for good. The vet's latest theory is that she's allergic to humans (hahahaha doh), and acarians (her condition improves for a while when we do a big spring clean). From time to time we have to put a collar on her, just so all the scabs can heal. It also helps to clean the affected areas regularly & put cortizone cream on. In any case it's in no way transmittable to other animals (we have another cat & a dog, they're both fine).
Good luck & if you find a miracle solution let me know!