" A. apis, (the fungus that causes chalkbrood)  produces
a substance with antimicrobial proprieties.  The agent
found in chalkbrood that suppresses AFB was found to
be the fatty acid, linoleic acid. "  endquote

I think that the antimicrobial properties must not be effective on the
EFB bacteria.   I have frequently seen hives dying with both EFB and 
chalkbrood.   Both seem to be opportunistic when bees are stressed.
I also associate both with low adult bee numbers.

Stan

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