Does fumagilin-B hold down dysentery? No. It specifically states on the bottle it is used for nosema.
Does dysentery have anything to do with nosema? While nosema causes dysentery, dysentery is not always caused by nosema.
Now stay with me.....Have you ever taken 10 days of antibiotics? Maybe for Lyme, or some other problem. Many people when taking antibiotics, (and I know I do) come down with the runs. Those same antibiotics that kills the harmful diseases being targeted, also kills off the good stuff like enzymes, beneficial bacteria, etc.
Before CCD rolled around, a few people were looking at the impacts of such broad based medications, and the impacts of changing the gut makeup within the bees.
Except for one year when I treated one yard to compare to the other yards, I never treat for nosema. I maybe have 1 hive in 50-100 that gets the craps. And I have never had a problem with nosema even though I have had my bees tested several times over the years.
I don't feed sugar syrup in the fall except for a few hives. And that is from platform feeders that are emptied by bees actually able to process the syrup every day. I think hive top feeders that allow bees to feed 24 hours a day might be bad for several reasons including excess moisture in the hive promoting mold, etc. I have also seen many situations of others where syrup is more than a few days old and is moldy. (If you actually see mold growth, the syrup started going bad long before that time.
As with most things bad in the hive that causes loss, this is one of them that I feel is advanced by bee management.. Poor feed, blasting the bees with antibiotics, and other factors all play into very unhealthy situations.
You fed with fumagilin so nosema should not of been the cause of dysentery. So you as the beekeeper need to think of the reasons why they have it. Poor feed, moisture and other contributing factors....or perhaps the feeding of medication itself played into it.
I have never seen in the field studies by beekeepers (not the manufacturer or some paid university level grad student who is seeking funds). My own testing showed no difference in dysentery levels, and no difference in overwintering rates of hives treated and not treated.
If you scan down to the bottom of this link page, you can see my hives without and treatment, and the overall average of other beekeeper hives, many of which had been treated with fumagilin.http://www.bjornapiaries.com/researchatbjorns.html
Your bees had the runs. Probably not from nosema. So the question is why?
I hope this helps.