Thankfully, I can't talk as a man with experience on the matter, but from the literature I would say that Baker is on the right track. I would give them a decent dose of fumagillin as soon as possible.
the reason for return bouts with diarrhea probably has to do with equipment that hasn't been adequately cleaned. During the spring and summer season, with a lot of egg laying by the queen going on, the colony keeps ahead of the infestation, but as things slow down, it breaks out.