Zombies and Cannibalism: the spread of an epidemic

OMG ZOMBIE POST!!!
Let’s all pause and contemplate how awesome I look as a zombie. I DO love brains. Very much. OM NOM NOM.
So Sci was thinking about what to post for Zombie Day. She thought about wondering if dogs could sniff early stage zombie infection and thus help with quarantine. She thought about whether or not grocery stores would be a good place to hide, but Evil assured her that Costco is better (everything is better when you buy IN BULK!). She then thought about maybe finding a disease or mental problem that made people crave human flesh.
And then she went, holy crap that is AWESOME.
And then I abandoned that one paper I was going to write about wasps, which is ALSO awesome, but will have to happen another time.
Because we usually think of a zombie epidemic as being something that would occur via a viral or bacterial infection, which would then cause the victim to become undead and then go about seeking human flesh (or brains, but apparently the fixation on brains alone is a relatively new phenomenon in the zombie mythos).
But what about the cannibalism itself, the whole seeking after human flesh bit? What if a lust for human flesh could arise from…eating human flesh? As, say, in a scenario where starvation was forcing people to cannibalism, and thus the massive social taboos against cannibalism are relaxed? And then…all you’d need is a disease that spread VIA cannibalism. Like kuru, only this would involve MOAR BRAINZ.
So this post has two aspects to it, the prospect for spread, and the prospect of a way to eliminate the zombie menace.
Rudolf and Antonovics. “Disease transmission by cannibalism: rare event or common occurrence?” Proceedings of Biological Science, 2007.
I would also like to note that killing people and eating them apparently sounds a lot more scientific as “interspecific necrophagy”.

Anyone who looks at the animal kingdom knows that most other species don’t really have taboos on the subject of cannibalism (especially insects, those dudes will eat ANYTHING). This is a different sort of predator-prey interaction, and one that’s going to have a very significant effect on a given species’ population.
In humans, there are actually two DIFFERENT types of humans eatin’ each other with a nice Chianti. The first is actual cannibalism, why the second is ‘intraspecific necrophagy’. What’s the difference? Well, in cannibalism, you actively kill and then eat the person, while in intraspecific necrophagy* the dude is already dead, and you just HAPPEN to eat him, usually in a very ritualistic manner.
And you might say, well what does it matter if he’s dead first? In terms of things like potential disease spread, it actually matters a great deal, and we shall see why.
So for this study, the scientists wanted to form a model of disease (like say, a potential ZOMBIE disease) spreading through a population via cannibalism or necrophagy. They found only two diseases were spread by cannibalism (one of them was kuru and the other was in a lizard), but there were a bunch of other diseases spread by necrophagy (one of which was ALSO kuru).
They then came up with a model that contains a lot of math to look at the spread through the population. The variables included the number of people susceptible to the disease (which comprised the total population, the birth rate, and the possible increase in birthrate gained from cannibalism or necrophagy due to increased resources), the LOSS of the people susceptible to the disease due to death via cannibalism, loss of people susceptible via being infected with the disease (ZOMBIES), and the rate of change of the number of people being infected (which would include death from the disease, but in the zombie case, I guess it wouldn’t because they NEVER DIE). They also include the number of susceptible people sharing one cannibalistic victim, the probability of disease transmission from the cannibalistic event, and the number of victims killed and consumed per unit time. The whole thing ends up looking like this:

Sci’s not a specialist on this equation, but you can get the basic idea.
S = susceptibles
t = time
I = number of infected
b = birth rate
e = energy loss due to trophic transfer when you eat the guy, this is also the increase in reproduction due to the abundance of delicious dude meat
a = attack rate
N = the total number of the population infected + susceptible
g = number of people eating
small sigma signal thingy = transmission rate
small italic d (not the regular d for change) = disease independent death rate
v = death rate due to cannibalism disease infection per unit time (in the case of zombies this would presumably be zero, with a corresponding increase in the number of susceptibles in the form of those eating brains but unable to be reinfected, which would add another variable to the equation near a and g, we will call it variable z)
See? Simple!
The important variable I want to look at though is g. That’s the number of susceptible individuals sharing a carcass, which creates a possibility for the carcass to infect multiple victims rather than just one. And this is important because, as the equations above show, this disease (zombie or not) isn’t going ANYWHERE if the attacker/victim ratio is just one to one. More than one person has got to dine on that carcass. And really, that makes more sense, I mean, I know a regular sized person is far more than I can eat in a meal, and storing it is presumably not an option (now a small child, maybe if I was really hungry).
So you’ve got to have a group eating. The spread of the disease through cannibalism would also be increased if infected individuals themselves were more likely to be eaten (slower, sicker, etc). So the disease could end up spreading pretty well.
BUT, this equation (and a couple of others that they present) tells us one other thing: the disease CANNOT wipe out the human population. See here:

This is a graph made using the modeling in the paper. You can see that the disease can invade substantially, but part of the human population will be safe. Even with necrophagy rather than active cannibalism (they had separate models for this), the disease still couldn’t spread to the entire human population.
The net result was this: cannibalism itself, the violent method, often involves a one to one, and so probably wouldn’t be as effective. Necrophagy (as with kuru, for example) would be more effective due to the greater likelihood of group consumption. But this is not necessarily uncommon, and necrophagy or cannibalism could possibly contribute to the spread of things like kuru, and also to the spread of some blood-borne disease.
So that’s the paper. Let’s talk zombies.
So in Sci’s version of this zombiepocalypse, the zombie epidemic will follow something like a massive war or crop failure, which leaves large numbers of people starving and willing to eat their fellow homo sapiens. One of the diseases transmitted this way would be the zombie disease, in this case maybe a sort of prion disease or blood-borne pathogen that would infected the cannibals (or necrophages). And this disease would involve the insatiable desire for more human flesh.
So let’s say that a zombie in possession of brains must be in want of more brains. This disrupts the whole scenario in the paper, in that you don’t have a natural death rate of infected individuals, instead you have a steadily growing group of people wishing to feed upon the carcasses. This really messes up the entire scenario, because the people who feed upon the carcasses have a greater reproduction rate, and also decrease the susceptible population because they cannot be reinfected. So I think (though I admit I didn’t do the math myself and would welcome someone else to do it!) that in cases where the death of the infected = undead, the results MAY actually kill off the human species.
But, there’s a solution.
So Sci’s been reading this AWESOME new book out from Deborah Blum, called “The Poisoner’s Handbook”. I absolutely recommend it, it’s fantastic. And it got Sci to thinking about ways to poison zombies.
See, if you can find a way to dispose of the zombies by chemical means, you could lay out lures. Lures in the form of, say, freshly poisoned humans willing to sacrifice for the greater good. If that’s too icky (probably for a group already practicing cannibalism it’s not), you could also leave already dead human meat out laced with poison for the zombies, or alternatively find a means of keeping the dead meat warm, if the zombies are only attracted to WARM human flesh, to simulate a live body. If you get a whole group of zombies feasting, this effect could kill a large number. Of course, it would take a lot of poison and a lot of flesh, but if you got it started before the problem became large scale you could stave off the development of an epidemic.
Also, avoid eating human flesh. I hear you can catch stuff that way.
Rudolf VH, & Antonovics J (2007). Disease transmission by cannibalism: rare event or common occurrence? Proceedings. Biological sciences / The Royal Society, 274 (1614), 1205-10 PMID: 17327205
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*Side note: So Sci is a musician and was really in to musicals in her high school and college days, and her friends were really into it as well. One time, a friend of mine (hi Matt!) and I, both of whom had gotten FAR too little sleep during finals, were sitting around in the coffee shop at 3 in the morning (I still remember my copy of Philosophical Investigations being open to page 162), and decided that we needed to write a hilarious, tongue-in-cheek musical about necrophilia, Mel Brooks style. We were going to call it “Necromance”, and it was going to be about a necrophiliac who works in a morgue, and falls in love with a beautiful body that turns out to not really be dead. The opening number was going to be called “I’ve never felt the warmth of love”. That’s about as far as we got with it, but it occurs to me that there needs to be a patter song in it, a la Gilbert and Sullivan, that rhymes the words “intraspecific necrophagy”. Something like “My love is innocent, don’t think I’m cagey/not into intraspecific necrophagy”. True story. And now you probably know WAY more about the inner workings of Scicurious than you ever wanted to know.