I have a boot dip outside my chicken shed.
The main spread is through water so obviously waterfowl are most at risk and most likely to be the carriers that spread it elsewhere.
I have 4 semi-feral geese and 5 muscovey ducks who, I'm afraid, have to take their chances. When I feed, it's under cover and stand by to keep wild birds away, but like others here, the water is from a stream and I have no choice in that as there is no other water supply. I simply cannot humanely shut them in because of their location (on top of the moors in a very remote field) and semi-wild state. I will cull rather than shut them in, if I can catch them, but really hope it won't come to that.