Hi Carmenie,

Well AFB can be spread from robbing or drifting of bees.  However, since
your hives where used and I assume you didn't know why bees where no
longer kept in them then the spores may have been in the equipment.
Since you have burnt one hive.  Watch the remaining hives this spring.
If it shows up again in my opinion you have 2 choices.  1. Burn the
hive. 2. Move the bees in to a completely new hive with fresh foundation
and feed heavily with fresh syrup.  Leave all the brood and  honey
behind. Burn them then bury the remains.  The spores are passed to the
larvae in food.  By the time the queen has cells to lay in the bees
should have used up any food they may have had with them.  I would only
do this if there are enough bees to make it worth while. Just my
opinion.  Good luck

Kent
Kingston, Ontario