The virus is a mystery, best explained by the fantastic and fantasy. However, for this thing to be real we need some real possibilities, some real science. To bridge that gap we must have brain activity. Without that we turn to "There is no more room in hell theory" or perhaps Aliens. I still like the virus theory. True, it takes more thinking, exploring... unraveling the what could be a very real viral outbreak.
The virus effect its host much like a stroke victim. As the virus infects the host, it secretes its digestive fluid into the host creating a breading ground for more. Its secreted fluids act both as a protective enzyme, both killing bacteria, and preserving the host. Yet in the early stages, the virus travels up through the blood brain barrier into the thalamus. The virus is attracted to axioms. Neural Electric Chemical Activity found in the hypocampus.The very spark that gives mobility to the central nervous systems, and other motor functions of the body. One drastic effect the virus has is the ability to kick start its host back into undead-life, using its own Bio Electric field. By damaging the balance of the thalamus where the most primitive actions come from - thirst, hunger, sexual arousal, all are computed here. The virus some how knows this area of the brain contains the main function of its host' appetite. And by taking unhinging the balance of the thalamus, the virus is able to feed itself on new bio matter from it's host insatiable appetite. .
The virus also has a provocative action which has remained a mystery to this day. The virus emits a much more stronger BEMF (bio electric magnetic field) than found in cold blooded species. It senses bio-rhythms. This is how the undead are able to track their victims; through their victim's BEMF's. In larger groups the undead's range is magnified. much like sharks detect their prey, while other species use sonar or electrical emissions. the undead, in larger groups can detect life up to 5 mile away. As sharks do not have anus' they excrete their waste through their epidermis. The undead do so the same. Since the virus is bio electric, the viruses own BEMF also allows the undead to identifying potential bio matter for its infestation pool; Thats is why the undead do not eat dead bio matter. They do not eat each other or themselves.
If you have anything further to add to my theory, shoot me a line. I believe the science is good.