Most zombies have a chance to spawn with a special trait - Feral or Radiated. A Feral zombie will have glowing orange eyes, increased health, deal more entity and block damage, and may have a different speed depending on the game's Zombie Feral Speed setting, along with faster animations in general (waking up, attacking, recovering from a fall, etc..).
The Burn Victim is the only zombie unable to have the feral trait.
Feral zombies can be fought almost exactly the same as normal zombies since they fight exactly the same; unless their speed has been changed. If the game's Feral Zombie Speed is set to Jog or higher, fighting feral zombies requires more caution as they can catch a survivor off guard with their speed. Due to their high health, using a high damage weapon and/or taking advantage of stealth bonus damage proves highly effective when dealing with feral zombies. If their speed is a problem, dismemberment, traps, and staggering (also known as ragdolling) can help to slow them down and make them easier targets for attack.
Feral zombies have nearly twice the detection ability of their normal counterparts, making them much more difficult to sneak past and almost guaranteeing their presence when using a loud vehicle. Like with normal zombies, this can be mitigated by having a lower Noise stat (see: Stealth System), moving slowly, staying out of light and trash piles, and investing skill points into the From The Shadows perk, under the Agility skill.