This week the Countdown Team found a better, and more horrifying, explanation of the apocalypse than anything we could find in the news. So, here is a list of actual reasons a zombie apocalypse could occur. Remember the fifth world begins in 2012.
Parasites that turn victims into mindless, zombie-like slaves are fairly common in nature. There's one called toxoplasmosa gondii that seems to devote its entire existence to being terrifying.
This bug infects rats, but can only breed inside the intestines of a cat. The parasite knows it needs to get the rat inside the cat (yes, we realize this sounds like the beginning of the most fucked-up Dr. Seuss poem ever) so the parasite takes over the rat's freaking brain, and intentionally makes it scurry toward where the cats hang out. The rat is being programmed to get itself eaten, and it doesn't even know.
Humans and rats aren't all that different; thats why they use them to test our drugs. All it takes is a more evolved version of toxoplasmosa, one that could to do us what it does to the rats. So, imagine if half the world suddenly had no instinct for self-preservation or rational thought. Even less than they do now, we mean.
Nanobots are a technology that science apparently engineered to make you terrified of the future. We're talking about microscopic, self-replicating robots that can invisbily build--or destroy--anything. Vast sums of money are being poured into nanotechnology. Sure, at some level scientists know nanobots will destroy mankind. They just can't resist seeing how it happens.
Scientists have already created a nano-cyborg, by fusing a tiny silicone chip to a virus. The first thing they found out is these cyborgs can still operate for up to a month after the death of the host. Notice how nano scientists went right for zombification, even at this early stage. They know where the horror is.
According to studies, within a decade they'll have nanobots that can crawl inside your brain and set up neural connections to replace damaged ones. That's right; the nanobots will be able to rewire your thoughts. What could possibly go wrong?
The nanobots will be programmed to self-replicate, and the death of the host will mean the end of the nanobots. To preserve themselves, they'd need to transfer to a new host. Therefore, the last act of the nanobot zombie would be to bite a hole in a healthy victim, letting the nanobots steam in and set up camp in the new host. Once in, they can shut down the part of the brain that resists (the cortex) and leave the brain stem intact. They will have added a new member to the unholy army of the undead.