I would have to think mites. I think soaking would be good, as well as trying a thick coat of 3x antibiotic ointment applied going against the direction of the scales. Aside from mites, the mites may have caused easy entry for infection. Aside from the soaking and ointment, I would powder the chicken well with Sevin or poultry powder, esp the fluff at the top of the legs and the underside. Aside from going to the vet, I think it's a matter of making a list of possibilities, then maybe the process of elimination.