Apart from beekeeper action, the usual reason for the spread of EFB is  
drifting of bees between colonies.  How close together are your  hives?  Are 
they arranged in rows or scattered?  Are they uniformly  coloured or rainbow 
shaded?  Are they on a mown sward or arranged among  bushes or other 
landmarks?
 
In times of prosperity (lots of nurse bees and a good income) EFB often  
goes unnoticed by the beekeeper as there isn't heavy mortality and the bees 
can  easily clean up those that do die. The corpses can be removed whole by 
the bees  without passing on the infection. In times of prosperity, infected 
larvae get  enough food to enable them to pupate successfully, but still 
carrying the  infection which they pass on.  The symptoms you see: misshapen 
larvae  usually, are those of starvation as the bacteria out-compete the larva 
for the  food supply.
 
As far as I know, I have had it only once, in July 2000. I spotted a couple 
 of larvae looking uncomfortable in their cells in a nucleus.  I called the 
 bee inspector at once. He took a look and told me he thought it looked 
more like  sac brood, but took a sample for the lab anyway. The sample proved 
positive for  EFB.  That was at the time when treatment with antibiotic 
(Aureomycin)  rather than burning first became permissible in the UK.  The 
Inspector  treated them while I was away at Gormanston and when I came back I 
found in the  hive the green dye with which he had mixed the syrup.  The nuc 
weakened and  died anyway.  Of course I kept a close eye on the other 6 nucs in 
the  mating apiary but none showed any sign of EFB.
 
It appears that there may be some strains of bee that may have some  
resistance to EFB.  A retiring professional beekeeper once told me that,  after he 
had brought all his hives back from pollination contracts and had  gathered 
them together in a holding yard, he found EFB in one hive.  It  took some 
time to arrange a massive bonfire and he couldn't move them away  because 
there was a 'standstill order' on the apiary.  In the meantime the  EFB very 
rapidly spread from hive to hive and was everywhere except in one  particular 
hive that never showed any sign of it; but it had to be burned with  the 
rest.
 
That is one reason why I number my queens rather than my hives.  If I  make 
the time I can provide a 'family tree' on the female side of those that  
didn't arrive with swarms this year, just in case any heritable qualities, 
good  or bad, show up.
 
Chris
 
 

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