Fromhttps://journals.plos.org/plosone/article?id=10.1371/journal.pone.0263602,
what I found to be of interest was:

" Surprisingly, of the three operations asked to select an unaffected
apiary free of AFB, only operation A was successful in identifying an
apiary that concurrently had a relatively low degree of spore
contamination. Although the unaffected apiaries in both operation B and
operation C were free of clinical signs of disease, they still had
individual hives with levels of spore contamination comparable to those in
the index apiaries. Based upon spore thresholds for clinical AFB in other
studies, it is reasonable to expect that very high concentrations of spores
in these seemingly healthy hives would likely be associated with the
presence of clinical/subclinical AFB if not for the recent and/or continual
application of antibiotic therapy. This raises concern that beekeeping
operations, through the chronic use of antibiotic metaphylaxis, may
underestimate the severity of contamination within their operations"

The above is what I realized many years ago, so stopped prophylactically
applying antibiotics, and instead adopting a zero-tolerance policy for AFB
-- burning all the combs of any infected colony.  Otherwise, there is a
constant reservoir of spores in your operation, just waiting for the right
conditions to rear AFB's ugly head.

The curious thing is that most of the California beekeepers that I know
haven't seen a case of AFB in many years, and we all wonder why.  I have
seen it in urban areas full of treatment-free beekeepers, and it was
brought to our county a few years ago on some borrowed honey supers from
Montana (where I've also seen it in commercial operations).

In our own operation, despite going to almond pollination every year, we
haven't seen a single case in close to 20 years (knock on wood).

Randy Oliver
Grass Valley, CA
530 277 4450
ScientificBeekeeping.com

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