Odd isn't it. It seems reasonable for chickens to have a predisposition to certain health problem much like other species. It's also worth bearing in mind that much of the medical advice regarding chickens is aimed at the commercial sector where it's easier to cull than treat.
I don't know. It doesn't seem to be a case of breed. I've had Bantams where the problem arose every other generation on the male side only. I've had Black Minorcans where some hens got it and some didn't but I didn't know the parentage so couldn't follow the genetics. I've had Marans Bantam...
I'm just going to copy and paste a post I made on another thread where the matter of scaly leg mite cropped up.
"I've dealt with a lot of Scaly Leg Mite. I've been writing about it on this thread recently. Henry has it. He's had it most of his life. His daughter Matilda had it. His daughter Mow...