The cure has been well covered. Prevention? Never put shoes (or anything else) in a constricted area (shoe cupboard/shoe box), if there is even the slightest damp on them;-that includes any foot sweat (sorry!!). Sprinkling some talcum powder inside refreshes them. Come to think of it...., after thoroughly brushing the dry shoes, liberally sprinkling them with talc;-rubbing it in;-then brushing it off will help/solve? the mould problem.