Wierd scab on back above tail feathers

[handsomecock]

So can anybody tell me what this is exactly? It appears to me as of she or one of the other chicks was pluckin her feathers. Either that ir they fell out. Maybe she was acratchin it or somethig becuade it feels scabby to the touch.

 

[BettyBlueSilkie]

could be a case of foul pox

 

[fluffychicken24]

What do the scales on her legs look like?

 

[handsomecock]

The scales on her legs are fine. She's a cochin so she has feathers there and they look good. Will check to be certain when I get home. What could it mean? Are the other chicks at risk?