The zombies in The Walking Dead are caused by a fictional virus that reanimates the dead.

In The Walking Dead, the cause of the zombies is a fictional virus known as the “Walker Virus.” This virus is believed to have originated from a combination of factors, including a mutated strain of influenza and a parasitic organism. When a person is infected with the virus, it attacks their brain and nervous system, causing them to die. However, instead of staying dead, the virus reanimates the body, turning it into a mindless, flesh-eating zombie.

The Walker Virus is highly contagious and can be transmitted through bites or scratches from infected individuals. Once a person is infected, the virus quickly spreads throughout their body, shutting down their vital organs and reactivating their motor functions. The infected individuals lose all sense of humanity and become driven solely by their primal instincts to feed on living flesh.

It is important to note that the virus does not discriminate and affects both humans and animals. This is why we see various types of zombies in The Walking Dead, including humans, dogs, and even horses. The virus has also been shown to affect individuals differently, with some turning into walkers almost immediately after death, while others take longer to reanimate.

The exact origin of the Walker Virus is not fully explained in the series, but it is suggested that it may have been a result of a government experiment gone wrong. The virus spread rapidly, leading to the collapse of society and the rise of the zombie apocalypse depicted in The Walking Dead.

Overall, the zombies in The Walking Dead are caused by the fictional Walker Virus, a highly contagious and deadly infection that reanimates the dead and turns them into mindless, flesh-eating creatures. The virus has devastated the world and is the central threat in the series, as survivors struggle to stay alive and find a cure or a way to prevent further infection.