Although this is not the forum of my interest ( I live in Greece ) i noticed the title of the post in the first page. Have you ever tried the shaking method ? Do you kill all colonies found to have AFB ? How many frames bees cover in these beehives ?http://postimg.org/gallery/59r4z82w/
This is a small colony that was shaked 2 days before photos taken to frames with only a part of foundation. The queen is laying. After a few days you can see the quality of the brood. Last year i "cured" 3 colonies from AFB that this year are productive. Of course killing the colony is 100% safe, but a shaked colony has fewer AFB spores compared to the rest of established colonies.