How do i get rid of scratches on my horse?

I noticed the other day that my horse had a open sore/cut on his hind fetlock. after touching it i noticed all of theses scabby bumps on the back of both of his legs next to the sore. Naturally i washed it up with some betadine but i need to get rid of this asap. I heard that it can cripple your horse if not taken care of correctly. I wont pick them off either because another horse in the barn has had a staff infection and i dont want any other infections getting in. does anyone have any advice on how to get rid of it? Thanks!