First, since I think everyone on earth deals with biting Midge Flies, I Googled "African Horse Sickness". http://www.cfsph.iastate.edu/FastFac...sickness_F.pdf
THAT is some scary stuff when one realizes it is probably spread a lot easier than anything mosquitoes carry around with them
The above link is dated 2011 and no incidents had been reported in the U.S. Give that some time----------------
Anyway regarding garlic:
I have fed equine garlic, seasonally since 2004, for tick control. It helps keep ticks off my horses to about 85% efficiency.
I honestly don't see that it does much for flies - especially house flies and midge flies
I live in SE United States where we have long warm seasons and more humidity than temperature in the summer. I generally start the horses on garlic in mid-March and don't have to start spraying them until late June or early July.
Meaning, I honestly don't know if the garlic helps to keep me from spraying that long or not; I know that the rest of my world are already going thru bottles of fly spray.
If you try garlic, do NOT feed raw garlic as it's the allicin (sp?) in raw garlic that can possibly cause anemia in horses. Processed/powdered garlic should be ok, unless you have a horse with digestive issues and/or is prone to colic.
Bacon Grease: Huh! Makes sense to me if you can put up with it on your horse
When I was a kid, back in the early 60's, we used bacon grease for wounds as it's we had available in our rural area - lol
I also wonder if something sulphur-based, like MTG, might work??? As long as the horse doesn't have any open sores since the sulphur would burn them. Also some horses are allergic to MTG so you would have to do a skin test before spraying.
Apple Cider Vinegar in the feed so it permeates thru the skin, like garlic would? You'd have to watch for the runny bums and again, I'd think twice if the horse has digestive issues.
Maybe some sort of smelly concoction of some or all of the above?
I'm out of ideas but I will wish you the very best of luck figuring this out and that your horses stay free of what is a horrible sickness