How far does fire blight travel?

I have a small orchard I spray for fire blight each year. I had a little problem with a couple of trees but mostly everything is in good shape. I have an ornamental crab apple about 100 feet east of my orchard and it has been hit hard with fire blight this year. When I cut out the fire blight in my orchard I take the cuttings and burn them. I am wondering if I have to worry about the blight on the crab apple? Should I cut it all out and burn it or can I just let it go?