can someone describe the "smell" of AFB?
The smell is hard to describe, unless you have experience working for a luthier who used hide glue.
Even though, as an inspector, I have walked into an apiary and known by the odor that AFB was there, identifying AFB by sight is something that beekeepers should do. For me, quite often, it starts w/ something being not quite right w/ the colony, which leads me to look a little more diligently at the brood combs. If I don't see anything wrong, brood wise, then maybe I was just wrong. But then looking at the capped brood, one might see sunken capping w/ an oily sheen and punctured cappings. Check out one or more of those punctured cappings and see if there is a brown viscus liquid laying against the bottom side wall of the cell. If so, stick a stick into it and it should rope sorta like rubber cement. That's AFB. 99% sure.
Another thing to look for, which I am doing right now as I put on some deep combs that I got last year, is scale. Scale can be seen in dry comb by holding the frame by the top bar w/ two hands, w/ the sun over your shoulder. Slowly tilt the frame by holding the top bar and raising the bottom bar untill you are looking across the open cells, but not looking straight into the cells, but at the bottom side wall of the cells. If you see a mass in a number of cells, a black mass, that is probably AFB. You won't be able to get the scale out of the cell w/out destroying the comb. Burn those frames.