I imagine this is scaly leg mites. Cover the legs with Vaseline, vegetable oil, Crisco -- anything that will smother them. Repeat daily til he's better. You can also wash them once before the Vaseline to speed it up a bit. Use a soft brush, mild soap and water, and scrub the legs gently, to get the soap under the scales. There are a bunch of threads here about scaly leg mites, both in Predators and Pests and Emergencies.