Last Sunday I checked the 48 hives that I installed last spring on
equipment that was salvaged from hives that had had AFB.  The frames were
ones that did not have scale, but which may have been right beside ones
that did.

The bees were three pound packages from Australia. They were installed,
and given one extender patty made as per my website (below) and never
treated at all again until this spring, one year later.

Of the 48, 8 died over winter -- for whatever reason.  There was no sign
of AFB in any hive, alive or dead, when I looked at them Sunday.  All the
other hives were clean.  Most were so strong that I had to reverse them
and -- in some cases -- add a third.

I realise that there are some concerns about extender patties, and also
some concerns about using antibiotics as agricultural prophylactics,
however I have to report that it works for me.

One patty a year (made and admistered properly) seems to do the trick.

In my experience, administering oxytet by dusting or syrup feeding can be
almost as effective, but either method requires many repeat visits.
Moreover,  the rate of failure is higher.  This results in much more drug
use, and continued presence of the spore forming stage of the disease.

FWIW.

allen

http://www.internode.net/HoneyBee/