I believe that this started in a Utah or Nevada horse show, or at least for the ones in our area. Several cases right around here.
Like she said, keep your large fur kids at home, don't allow any strangers who "LOVE HORSES" to touch them if they've been around others, especially in other states. I'm not too sure how this is passed, could be direct contact or air born, not too sure about that, but could be brought in on shoes or clothes.
It's best to be sure.