Foul brood has been around a long time.  In a 1568 book Nichel Jacob
wrote of "foule brut".  His treatment method was to cut out all the
honey and comb, then keep the bees locked up for 3 days starve all the
honey out of their coups.  He then took a new hive and put it on the
bottom of the stand setting his sick bees on top.  He fed them good
honey and said this always worked best when the "cherries were in
bloom".  Remember this was in 1568 before we had hives like today.  It
is interesting to note also that in Moses Quimby's book of 1853 gave the
same procedure, almost 300 years later.  At the time, AFB, EFB and sac
brood were all lumped together into one disease.  My point being that
this bacteria has been around a long time so why haven't we solved the
problem?   I think you can find the answer for this is "beekeepers
fears".  In the early 1900's when people would write about a solutions
to cure foul brood, they were lambasted in the journals by others who
insisted that fire was the only answer.    Inspectors also took this
opinion as there was fear of the disease moving from farm to farm.
Remember the time, every small farm had hives.   This thinking stifled
research.  Think of this, in the November 1905 Gleanings magazine a FW
Alexander wrote an article to report that he found some bees were better
housekeepers than others and related this to cleaning up foul brood.  He
advocated requeening or simply caging the queen to interrupt brood
rearing and give the hive time to be cleaned up.  That was 100 years
ago.  I think all we have done with years of prophylactic terramycin
treatment is hide the problem, its endemic to our bees.