Zombie apocalypses are a popular event in Hollywood because they speak to basic fears that we all share. Being the last person in the world with no one to turn to speaks to our fear of isolation. Being hunted by something almost human but not quite sets off our 'creepiness' radar and our fear of the unknown. The rotting limbs and leaking brains make real our fear of illness and ageing, and finally the idea that we could 'turn' if bitten, means we can't even trust in our own sense of identity – one of the few constants in any other crisis.
But fortunately most of us still aren't losing too much sleep over the idea for one crucial reason: they aren't real and aren't particularly likely to be real. After all, who could possibly survive with their face hanging off like that? (Plus there's the fact that zombies are like, really, really slow).
The bad news is that you may be kidding yourself. While there have been no known cases of real zombie attacks, the concept actually isn't that unbelievable when you look at some diseases and some naturally occurring phenomena. Let's take a look at just how close we could get to a real zombie apocalypse…
Diseases That Make People Like Zombies
One reason you might have to be a little weary of completely ruling out zombie attacks, is that there are a number of diseases that come scarily close to making zombies of their victims.
Take for instance the terrifying 'sleeping sickness' common in Africa. This condition starts by triggering headaches, followed by aches in the muscles and twitching. The condition is caused by parasites called Trypanosoma brucei that can get into the brain and which cause slurred speaking, lack of concentration and reduced appetite in the later stages. Eventually the patients are reduced to a 'zombie like' state in which they find it hard to complete tasks even as simple as drawing straight lines before finally entering a coma and dying. There is no vaccine available, and one of the only treatments available contains arsenic and often proves lethal.
One of the fundamental aspects of a zombie is the fact that the person is no longer alive. Rather they are re-animated or 'kept' alive by their disease. The person is no longer themselves, but rather a host for something evil.
This is the far-fetched part of the whole matter and fortunately there have been no recorded cases of people coming back from the dead and eating people. If your heart isn't beating and sending oxygen to your brain, then you aren't going anywhere.
However what is possible is for parts of your body to be technically 'dead' – for you to suffer with dead tissue that no longer sends signals to the nervous system or repairs itself. This is called 'necrosis', which can spread rapidly as enzymes are released by the dying cells. It is a terrible and distressing condition that can leave patients with limbs that look very much like they belong in a zombie movie.
Rabies is nothing you haven't heard of before, but you may not have considered previously just how similar it is to the classic 'zombie virus'. For one, rabies is transferred via bites from animals infected with the condition just like zombie viruses – and a rabid dog will act scarily 'zombie-like' in terms of its blood-lust. Likewise, the symptoms of rabies are similar to those portrayed in zombie movies – including mental impairment, aggression, mania and delirium. Fortunately, human-to-human transmission of rabies is very uncommon.
If early stories of zombie outbreaks were based on any real disease, then most likely that would have been leprosy. Leprosy is a well-known and highly serious condition that can lead to a similar slow-shuffling walk that could be considered similar to that of a zombie, as well as the outbreak of painful looking legions that give the appearance of decaying skin. And then there's the fact that leprosy is so highly contagious, which has historically lead to a lot of segregation and fear.
Interestingly though, the commonly believed idea that leprosy can cause limbs to 'drop off' on their own is inaccurate. While leprosy can create the need for limbs to be amputated due to numbness and lack of blood flow, there is no known condition that causes limbs to entirely detach themselves without help. At least that's one piece of good news…
The common cold might not seem to have much in common with a zombie outbreak and it won't give you any kind of urge to eat your own arm off. On the other hand though, flus and colds are incredibly difficult to stop and will spread quickly through a population. The flu virus in particular is well-known for constantly adapting and changing and will often threaten to turn into something more deadly. Remember the scares surrounding swine flu and bird flu?
In order for any illness to cause an actual apocalypse it would need to be incredibly fast-spreading, highly adaptable and completely immune to vaccination or treatment. The cold or flu don't quite fit those criteria, but they are certainly good examples of problems that man has struggled to eliminate. (Another example could be the black plague – an epidemic that spread so violently out of control that it took the great fire of London to finally put an end to it).
So where does this leave us? Diseases can't reanimate the dead but they can cause all manner of cell death and decay in living tissue. Some conditions can also spread very rapidly and easily and can even cause aggression in their victims as in zombie cases. On the other hand there are no conditions that do all these things, and none that cause super-strength and resilience or cannibalism.
More modern tales have thus taken this on board and tried to come up with more feasibly explanations for their conditions. Often that means blaming science and man's 'tampering'. Genetic modification is already possible to such an extent that a single injection can permanently alter your genetic code to give you super strength or transparent skin (it has been tested on mice at least). However the ideas that scientists could accidentally use insertional doping to turn a person into a zombie, that the necessary testing would ever be allowed are highly unrealistic. In fact this is probably more far-fetched than the idea of a disease bringing about the apocalypse.
Much more likely is that a zombie-like outbreak would be caused by a parasite affecting the brain. Sounds far-fetched? Then get ready to be absolutely terrified…
Toxoplasma Gondii is the name of a parasite affecting rats. What this parasite does is to affect the brains of rats and to switch off their survival mechanism. The parasites can only bread inside the intestines of a cat you see, so what they do is to affect their chosen rat's brain and then cause that rat to get eaten by the cat. The rat begins acting strangely and commits suicide without even knowing it.
You might think that nothing like this could ever happen to human, but then that's probably because you didn't know that half the human population is infected with toxoplasma and probably doesn't know it. And while the parasite doesn't drive those people to get eaten by cats, studies have shown that it may be responsible for subtle changes in behaviour and an increased likelihood of mental disorders. Now that's scary.
So imagine that this parasite were to undergo some kind of mutation (through man's tampering with nature if you like… sure, why not?), and to then achieve the ability to affect the human brain. It could then insert itself in our brain stem and affect our nervous system, undoubtedly causing strange and disconcerting behaviour along with deterioration of our health.
I'm not saying that it's making zombies out of us yet, or that it would ever create anything much like a Resident Evil situation… but then again if we were ever going to see a demon hoard it would be more likely due to something like this than any flesh-rotting virus.
Then again if you want to see real zombies right now, just take a look at the underground during rush hour…