A fungus? Has the weather been hot and humid or damp? Just guessing on my part, I've never seen it before.
Fowl Pox usually starts with a pearly pimple then crusts over.
Looks fungal to me. Is there any way their feed or bedding could have gotten moist (even from humidity)? If it is fungal, foot creams or monstat (sp?? the female cream) will work wonders.
Fowl pox is usually on the face comb and wattles.. I would discredit that statement. It may be scaly leg mites? I haven't personally had experience with those though.