A common question with commercial beekeepers these days is "What the heck
happened to AFB?"  It used to be a huge problem, but for many of us, has
simply disappeared.  My last major burning was well over a decade ago, and
I have not used prophylactic antibiotic treatment for longer than that.

I used to select for freeze-killed hygiene, but gave up on that once varroa
became my major problem, so haven't tested my stock for that trait in years.

So although AFB is a very rare problem for me these days, I'm well aware
that there is a raging epidemic of it in California's Bay Area recreational
beekeepers, and that some commercial operators are also plagued with it (I
just knocked on wood).

In my experience, AFB is difficult to spread, unless one transfers infected
combs, or allows infected colonies to be robbed out.  Colonies typically
appear to be able to handle low levels of exposure to spores.

Here's a snip from an abstract
<http://www.tandfonline.com/doi/abs/10.1080/00218839.1994.11100873> by Mark
Goodwin:
Twenty-five pairs of honey bee (Apis mellifera)
colonies were established with the hives in each
pair touching and the entrances facing the
same direction. One colony in each pair had a
light American foulbrood (AFB) infection «50
larvae with clinical symptoms) while the other
(control) was uninfected. The pairs remained
together for 5-388 days (average 103 days).
Any heavily infected colonies « 50 larvae with
clinical symptoms) were removed from the trial.
Only 2 of the control colonies developed AFB.


But back when I was selecting for AFB-resistant bees, I noticed that the
disease would reappear in colonies when they suffered nutritional stress.
This brings me back to my axiom:  Control varroa and provide good
nutrition, and most bee problems go away.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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