As someone else said it's not viral or bacterial because it wouldn't move that fast and you would be infected by now. A predator could easily reach thru your chicken wire window, but not sure they would want to stay suspended hanging with one arm. There would also be some damage or at least bending of the chicken wire. If a raccoon could get close enought to grab or bite, your chicken would be dead or at least more damage than just having the beak removed. Most predators would do the opposite of what is happening, rip the head or face off and leave it and take and eat the body.