Just supposition but if/when you find a large kill you might want to check out local Sheep herds.

We had no Blue tongue at all as far back as anybody could remember until a Sheep herder brought a flock of Sheep through our lease. There may or may not be an association, but I've never been a big believer in happenstance.

Is it possible domestic flocks or Cattle help transmit the disease to unaffected areas and/or more susceptible hosts like Whitetail?

Only two things I can think off to slow down the disease, is culling infected animals and spraying fly brood areas. The stock answer here is to seriously thin out the Deer herds for most kinds of disease and try to slow down the transmission cycle.

Many variations of EHD my thinking is it may be like the flu, constantly evolving.

Maybe one reason we have so few cases here is they spray for Mosquitoes intensively here. I imagine the same spray works on Midges. Maybe the Roe and Red Deer aren't as susceptible? Maybe it is because we rarely let the Deer herds over populate which slows down the Deer to fly to Deer cycle.?