We had a beekeeper recently contact us about his concern that some of his combs in storage may be infested with American Foul Brood (AFB). AFB is a bacteria that infects larvae through consumption of the brood food. An infected larva dies shortly after its cell is capped and turns into a brown, stinky goo. You can read more about it here, here, and here. If the diseased brood is not cleaned out, it hardens and becomes a dark brown scale on the bottom of the cell (see picture). AFB scale can be found in stored equipment or live colonies.
While the infected brood is dead, the scale still holds the highly infectious AFB spores. The best treatment is burning the frames. If found in a live colony, all the frames should be burned and boxes, cover and bottom boards scorched if not burned to avoid infecting other colonies. You can save the bees by shaking them into a box with foundation and feeding sugar syrup. Burning is highly recommended because the AFB spores stay viable for decades, acting as a source for re-infestation.
It can be a little tricky to be confident that what you see in the comb is actually AFB. One way to diagnose AFB scale is to use a black light. You can buy a little black light flashlight (see picture) online for easily under $20 – search “blacklight flashlight” on Amazon.com or any other shopping site.
To detect AFB, all you do is turn on the flashlight and shine it on what you think is AFB scale. If it glows a greenish-blue (see picture), then the comb has AFB and you should burn it. Other substances made of protein will glow as well, so be careful that you are looking at something shaped like a scale and not something else. Scales will on the flat on the bottom of the cells – picture a larvae melting and sticking to the bottom of a cell.
Jim Kloek has a great blog about this as well.