At first I thought it was a joke.
No such luck. Poor things.
What causes that kind of an epidemic? Foxes are quite solitary for canids, except when raising families. Do the mites live in a semi-dormant state, waiting for the next host, like ticks?
Is there a similar infestation problem appearing among domestic dogs in the region? I assume, of course, that owners of dogs afflicted with mange would seek veterinary care, so their dogs wouldn't come anywhere close to the awful condition this animal had reached before it was shot.