Foulbrood is caused by a spore-forming bacterium Paenibacillus larvae...ingested by bees as they visit sources of nectar. The article I read did not say where these bacterium live, what the host plants are.
It sounds like the stanglebrand of the bee world. Not something you want to find in your hives.
Let us know what your friend says. And what his source of information is.
