Did you know that there is research showing that being exposed to “spoilers” increases enjoyment of a story? True. Do I think you believe me or the research? No. In fact, I think you will treat this evidence with the same condescension political pundits applied to the predictions of Nate Silver. Furthermore, I think you will completely ignore the object lesson afforded you by the 2012 election forecasting. Is this the most overwrought and evidence-laden spoiler alert ever? Yes. You have been warned.
Let’s get the first major spoiler out of the way. At the end of The Walking Dead season 2, we discover that you do not need to be bitten by a zombie to become a zombie. You merely have to die. This leads to a lot of scenes of survivors sticking pointy objects into the brain cases of their recently deceased or mortally wounded friends in a practical act of mercy.
If you die, you kind of lie there for a little bit – just long enough for a father and son to share a moment – then you rise up and get your zombie on. This means that everyone in The Walking Dead universe has been exposed to the zombie pathogen. All survivors are carriers – zombies in potentia. This also means that the zombie pathogen is even weirder than it already had to be.
Being able to hijack the neurobiological kluge that is the human brain is pretty odd1 as it is. That the method of exposure seems to matter so much to how the pathogenesis progresses is even odder.
If the zombie pathogen is introduced via a bite, you almost invariably die. You die of a rapid onset fever. Then you turn into a zombie and eat the people who were lovingly tending to you.
If you ingest it, breathe it in, or just generally wind up with it smeared all over your mucus membranes while carving your way to safety through the zombie horde, you are fine. Exposure via any route other than breaking the skin causes the zombie pathogen to remain dormant, until you die of other horrible causes (with the exception of a .357 magnum slug to the noodle). Then you turn into a zombie.
This seems to suggest that the method in which you contact the zombie pathogen affects how it acts in your body.
To apparently contradict what I just said, my hypothesis is that the method of exposure is not important to how the zombie pathogen acts in your body, because there is more than one pathogen.
You might think that someone with my background would favor a system that requires only one pathogen. Under most circumstances, you would be right. The exception is when this would require the pathogen to behave in relatively extraordinary ways, in addition to turning dead people into zombies.
The first pathogen is, of course, the zombie pathogen2. This is the bug that actually hijacks the nervous system and causes the dead to shamble around eating everyone. This pathogen lies dormant until its host dies (perhaps as a method of avoiding the immune system) at which time it takes control of limited neural functions (eg, muscoskeletal control, hearing, etc). The zombie pathogen acts in the same way at all times: lying dormant until the host dies, regardless of the cause of death (with the exception of the aforementioned .357 magnum slug to the noodle).
It should be pretty obvious that I’m going to blame the feverish death after being bitten symptoms on the other pathogen or pathogens. Zombies are corpses, dead and rotting corpses. In the absence of efficient immunological defenses, human tissue can become the home for all sorts of nastiness. While a zombie bite can transmit the zombie pathogen (not very important once everyone is a carrier), it would also be likely to transmit a metric buttload of septic bacteria. You know, the kind of bacteria that can make you die of a brutal fever. It would not be shocking if that metric buttload of bacteria contained quite a few antibiotic resistant varieties. It would also not be terribly surprising if exposure to these bacteria without broken skin3 providing ready access to the bloodstream and internal tissues would not result in infection.
Details of horrible death aside, that infection kills the host and frees the zombie pathogen to take over. The zombie pathogen then compels the host body to shamble around biting people aiding the spread of the zombie pathogen and the nasty bacteria in a twisted form of symbiosis – or zombiosis, if you will (please don’t).
We can speculate that, in the beginning, the transmission of the zombie pathogen was closely linked to biting by a dead, rotting corpse, which meant it was closely linked to the acquisition of a lethal bacterial infection. At some point, the zombie pathogen started to spread without and in advance of biting. This need not involve a change in the zombie pathogen itself1,4, but could be the result of density (eg, prevalence of pathogen in water supplies5). The primary risk from zombie biting becomes the lethal infection, which can only be stopped by immediate amputation of the affected body part.
The use of amputation as an effective (if unpleasant) treatment for a zombie bite tells us that the zombie plague in The Walking Dead is meant to draw from the realm of infectious diseases, not the supernatural. And, that inevitably makes us wonder what kind of infectious disease it is, or in my case, wonder what kind of infectious diseases it are, I mean, they are6.
1. I’m on the record as saying that a zombie outbreak (particularly one that follows the Romero rules) is incredibly unlikely. Time spent planning for the zombie apocalypse is time wasted (though it can be fun). I am, however, quite willing to provide practical advice on the matter for a standard consulting fee.
2. I like to imagine that the zombie pathogen is a fungus, in part because I did some of my thesis work on yeast, which is a fungus. It is also because there are fungi that are known to hijack the nervous systems of insects. Imagine a fungus that grows on corpses, perhaps feeding off neural tissue. Hijacking the nervous system to “animate” the corpse, move around, and potentially infect new hosts could have an evolutionary fitness advantage. Likely? No. Plausible enough for sci-fi? Yes.
3. The fact that survivors are generally “roughed up” with abrasions all over the place when they are being splashed with zombie “ookiness” without dying of sepsis is a serious problem for any theories regarding the zombie plague.
4. Another reason to favor fungi – spores. Fungal spores are very resilient and can survive multiple modes of transmission. Emission of zombie spores could allow the remaining human population to be efficiently exposed once there are enough zombies producing them.
5. In Season 2, the characters are very concerned about contamination of a well on the farm by a zombie. After successfully extracting only a portion of the zombie, they decide to shut the well down. It is not clear if this is due to concerns about the zombie pathogen or just general fouling due to the presence of rotting corpse bits.
6. Strunk & White extol the virtues of parallel sentence structure. They also explicitly tell you that these are guidelines, not rules, that should be applied with judgement based on context and style.