My WAG on this, in places where it pops up out of nowhere and there are no game farms or other obvious vectors, that urine-based scent products may be the initial source. VA has banned all of them on suspicion. Don't know of any actual tests that prove it, but seems like a reasonable precaution, along with baiting bans in places where the disease already exists to slow the spread.
I'm located in a buffer zone. None here as yet, but it's not all that far away. My processor sends all the heads off for testing.
