What are Zombies from The Zombie Survival Guide and what is their importance?

Zombies are the subject of The Zombie Survival Guide. No zombie has any distinction or identity, but zombies taken as a group are fundamental to the novel. Zombies are people who have died of a viral disease called Solanum. Solanum kills a human host and then takes over the brain, replacing the human's neural network with its own structure. The Solanum virus then controls the undead human body, and the zombie is driven to seek out and eat human flesh that it cannot digest.