Alvin I too live in the PacNW and have heard the same things.

I attended two lectures a few years ago where each featured a local mobile pollination operator. They both stated they medicate their colonies prophylactically with oxytet to suppress foulbrood. They cannot afford the labour required to deal with and remediate foulbrood-stricken colonies or equipment. One can only conclude that this practice drives resistance. That may explain why EFB seems to be morphing into something more difficult to deal with.

I have often wondered if the old advice that a good flow clears EFB is accurate. I wonder if starving hives whose brood is also starving just do a lot better once the nectar and pollen start coming in. Perhaps their trouble was not EFB at all but simple malnutrition? 

When I see hinky brood (and the foulbroods are a common problem in my area) I use the Vita Life test kits to verify what I have. I have to date always found EFB, not AFB (alas this required the use of two separate $15+ test kits...). But twice I have found the tests on the affected larvae negative for both EFB and AFB. I have no idea what pathogen was affecting the brood in those cases. That may be the pathogen behind "tougher EFB" we hear of?

Which reminds me...the season is about to start, time to order fresh test kits. 

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