[ Joel lets out a breath, leaning against a nearby tree, crossing his arms over his chest. A defensive stance, in a way, because well - it's not exactly fun, explaining to someone how your world ended. When you lived through it. When you saw it. ]

It's called cordyceps. It mutated, somehow, and started infecting people. It doesn't kill you, though, or it doesn't just kill you. It eats into your brain, takes control of your body. Infected people get violent, start attacking people, biting 'em. Spreads it.

Nobody was able to stop it spreading.