Walkers

Walkers, or sometimes referred to as roamers, lurkers, biters, monsters, infected, and muertos, are an antagonistic force that serve as the primary catalyst for the events within The Walking Dead universe. They serve as universal antagonists.
==Overview==
Reanimated human beings, while not immortal, will not "die" under typical conditions that would ordinarily cause the death of a living person. They do not appear to feel or respond to pain, can survive even the most brutal injuries, and despite their bottomless appetite for flesh, they do not need food, water, or sleep to function.
They show no other bodily function that relates to a human, showing no signs of self-healing or response to extreme temperatures. The brain maintains limited abilities of the body, allowing for movement of the limbs (provided that they are not decomposed to the point where the bones are not strong enough to bend without breaking), jaws, neck, and even the use of its sensory systems. While the walkers are notoriously weaker than humans, the only way to kill one is to destroy the brain. Despite severely weakened frames, they will continue to hunt for living animals to consume. Even when decapitated, the head will remain active, even though it would be practically harmless at such a point.
===Transmission===
The virus pathogen seems to possess two separate, but parallel modes of infection: latent and fluid contact/bites/scratches.
*Latent: In The Walking Dead universe, most, if not every, human being on the planet is believed to be infected by a dormant strain of the pathogen. It is currently unknown how one contracts the dormant stage of the pathogen, though its apparent total infection rate worldwide suggests it is either air-borne, water-borne, or both. Once infected, the virus spreads throughout the body through the blood, likely concentrating in the central nervous system. However, so long as the host remains alive, the pathogen remains latent or dormant within them and is asymptomatic to the host.
* Fluid Contact/Bites/Scratches: Though physical contact with a walker's saliva or blood will not cause an individual fatal infection, any fluid contact with open wounds will lead to irreversible contamination of the individual. However, walker bites are not fatal because of the dormant pathogen. Rather, one explanation is that through bites, the active pathogen carried within walkers induces a fatal and irreversible cytokine storm, further exacerbated by bacteria that reside in a walker's mouth. Scratches could cause similar infections for similar reasons, however, no one in the series has ever gotten the fever as a result of a scratch. While walker scratches and clawing rarely cause fatal infections, the deep gouges generally left by walker bites are almost always fatal; death can be potentially avoided if the bite is on an appendage, which must be immediately amputated. However, this does not always work, and bites on the torso, or on veins or arteries are universally fatal. Even if an amputation proves successful at removing the infection, blood loss and subsequent infection are also extremely dangerous due to the generally unprofessional execution of the procedure.