Day 54: The Science Behind Real Zombies

Time for a break from stochastic processes, at least for the moment. Every year here we update and post our favorite Halloween tradition!  So today we bring you the science fact and fiction behind the undead. Zombies, those brain loving little things are everywhere. Sure, we are all familiar with the classic  zombie, but did you know that we aren’t the only zombie lovers out there? It turns out that nature has its own special types of zombies, but this isn’t a science fiction movie, this is science fact! Sometimes fact can be scarier than fiction, so let’s dive in. Let’s talk zombies.

Starting with Ophiocordyceps unilateralis, a fungus that can literally take control of ants. Once this happens it will climb down from its habitat, or after falling to the forest floor will climb underneath a leaf, and clamp down with its mandibles to secure itself to the leaf vein. This will be where the ant dies, in this “death grip.” Here is where it gets even more exciting (well not for the ant), the fungus breaks out of the ants head and spreads its spores. It makes the ant climb to the top so the spores can spread further than if the ant was on the ground.

Nailed it.

Not scary enough? Well it just so happens that the fungus doesn’t actually control the brain like we first thought! It does something much more sinister…

A team of researchers at Penn State University found that Ophiocordyceps unilateralis sensu lato, which is the specific type of Cordyceps fungus that infects carpenter ants (Camponotus castaneus), controls the behavior of its victims by only controlling their muscles. It turns out the “zombie” Cordyceps fungus leaves ant brains intact! They are literally turned into puppets and forced to watch as the fungus does what it wants.

That’s just the start, Gordian worms (also known as horsehair worms) can live in crickets for long periods of time. When this little guy is ready, it causes changes in protein expressions in the brain that make the cricket extremely thirsty. The cricket, basically possessed at this point, heads to a pool of water. This becomes the crickets watery tomb; it drowns itself simply trying to quench its thirst. This isn’t the end however, the worm exits the cricket to mate (hint: they live in the water). The children are then off to find their own unexpecting hosts.

Still looking for more?

Well let’s move on to something bigger, did you know that mammals can become zombies too? Even mice have their own zombie creating parasites to deal with. Toxoplasma makes rats lose their fear of cats — or more specifically, it causes the mouse to be attracted to cat urine. The mice, now out in the open, won’t run away when a cat tries to eat them. They have become too infatuated with the smell of that urine to care.

Being an extra clever parasite, this is exactly what it wants. When the cat eats the mouse, the Toxoplasma can then pass into the cat and mature. Afterwards, the cat passes it by its feces and the cycle continues.

Of course, what horror story would be complete without a sick twist? This little guy has even shown up infecting humans — and while it is thought to not have any effect  — it has been recently implicated in serious mental health changes like depression and even suicide. While nothing is conclusive quite yet, it would not be completely shocking — given the similarities between the mouse brain and the human brain — that it has some unintended effects that may not even be seen in the mouse models.

Not scared yet? Toxoplasma is a very common parasite… even in humans. If you’ve owned a cat, been raised with one, or even come into unintended contact with an infected cat… it may already be inside you. You read that right, it could be there now and you would not even know it. This is because, typically speaking, unless you are immunocompromised you would never notice you were infected by Toxoplasma.

Now usually the body fights back and takes care of the invader, but we still don’t know what the long lasting effects are from the infection. Heck we don’t know what the effects are in cases where the infection is only “temporary.” Unfortunately, even since we first started this post there hasn’t been any conclusive evidence one way or another. So like any good halloween monster, toxi is left open to make an appearance in the sequel. Does it affect humans at all? Only time will tell for sure.

Yummy, yummy cat urine!!

Not to be left out, snails get in on the zombie action too. Leucochloridium paradoxum (a mouthful I know), causes the snail to develop eyes that look like caterpillars. Snails, which prefer the dark, head out in daylight while infected, which causes them to be seen and consequently eaten by birds. Then of course, the life cycle continues.

I’m hideous!… ly delicious to birds.

That is not even all the examples that are out there (from the ones we know about). With all these actual zombies in nature, the real question is, what about humans?

What if some mind controlling parasite started turning us into brain eating zombies?

Well sadly for you zombie fans, besides the possible implications from a toxoplasma infection, there aren’t any zombie parasites that affect humans (that we know about, bwah hahahaha!). However, if you are one that just cannot wait for the zombie apocalypse, it would not be a surprise if something — possibly soon in a life of the earth timescale — could hijack a human brain… it may have already happened.

Human physiology is complex, but that complexity does not mean we are invincible, in fact it makes us more of a target. Think of all the nasty things that we have been going around already, HIV/AIDs loves to hijack the immune system (a smaller version of a zombie virus). Think of it like this, humans have very complex biology, but the more complex the system, the more ways there are to alter it.

The question is, what could come our way?

Well things like that are historically tough to predict. That is because when we talk about mutations in existing virus we have trouble guessing what would happen. That is why I wrote this post on the genetically created flu virus. Of course, there is the alternative, a genetically modified human-created virus that could do the job, perhaps something like in Extinction: The GMO Chronicles (which turned out to be a pretty good low budget flick IMO).

The movie revolves around a type of virus (they have one subtle hint it is actually a plasmid, those creepy, creepy things) that cross breeds genes from plants, animals and even humans. However, that kind of future would still be a ways off. Then again with old cold war style fears creeping back up again in politics, there might be something even scarier brewing for us on the horizon.

However, genetic engineering is super complex, it would be like me randomly trying to replace a single word in Atlas Shrugged, without the spaces to separate the words! It would be really hard to create something to replace the single word without accidently replacing all the other incidences of this word.

As an example, say I wanted to edit the “DNA” of this post (again without the spaces). If I wanted to replace a particular instance of the word “gene,” with the word “chip” it would be very difficult to do blindly and without replacing every instance. Furthermore, it would only make sense some of the time and the rest of the time it would just look like gibberish. Keep in mind DNA has only 4 different base pairs (4 letters) and it’s much, much longer — so the same strings pop up multiple times.

Using our book example, in some cases “gibberish” does nothing — maybe the sentence isn’t important, or is just some random detail. In other cases it could cause big issues — what if we accidentally changed the whole point of a book by changing that one word and suddenly Frankenstein’s monster turns into Frankenstein’s hunger.

This is unfortunately how genes work, most of the time if we edit something by mistake it will not do much (and that is a good case). Usually incorrect edits will cause cell death — or other really screwy things — because the gene we actually wanted to change also caused other instances of that string to be replaced and suddenly you’re a cell without the ability to code something needed to survive so you go into apoptosis.

Needless to say, we are dealing with very complex machinery. Personally, a gene swapping, zombie creating virus would be a scientific feat that is equal parts amazing and scary, but alas not likely to happen until we get far better at gene editing. So while we are well on our way, getting that good probably won’t happen in our lifetime… probably.

A little gene humor

Okay, time to break the news, zombies in the undead sense would not happen either (unfortunately for some of our hardcore zombie fans). However, humans with an insatiable appetite for human flesh, or even brains could happen. Scary enough, this would not even be that difficult to manage with right genetic modifications.

That’s because there already is a real life condition that has similar results called, Prader-Willi syndrome. This is a condition where you would not only have an incredible hunger, you would not be able to tell when you are full. People who suffer from the syndrome and don’t get professional help are typically dangerous, because having a constant hunger can, in fact, make pretty much anyone violent.

The bottom line is that while we should not worry about zombies anytime soon, it is fun to talk about all the weird ways things like this could happen. Frankly, if I had to guess, I would think nature would have it out for us before we got around to unleashing our own man-made genetic horrors.

In any case, whether we have a zombie apocalypse or not,

Happy Halloween!!

Sources: 

Fredericksen, M. A., Zhang, Y., Hazen, M. L., Loreto, R. G., Mangold, C. A., Chen, D. Z., & Hughes, D. P. (2017, November 21). Three-dimensional visualization and a deep-learning model reveal complex fungal parasite networks in behaviorally manipulated ants. Retrieved from https://www.pnas.org/content/114/47/12590.full

Lafferty KD (2006). Can the common brain parasite, Toxoplasma gondii, influence human culture? Proceedings. Biological sciences / The Royal Society, 273 (1602), 2749-55 PMID: 17015323

Vyas A, Kim SK, Giacomini N, Boothroyd JC, & Sapolsky RM (2007). Behavioral changes induced by Toxoplasma infection of rodents are highly specific to aversion of cat odors. Proceedings of the National Academy of Sciences of the United States of America, 104 (15), 6442-7 PMID: 17404235

Passamonti L, Crockett MJ, Apergis-Schoute AM, Clark L, Rowe JB, Calder AJ, & Robbins TW (2012). Effects of acute tryptophan depletion on prefrontal-amygdala connectivity while viewing facial signals of aggression. Biological psychiatry, 71 (1), 36-43 PMID: 21920502

Thomas, F., Schmidt-Rhaesa, A., Martin, G., Manu, C., Durand, P., & Renaud, F. (2002). Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts? Journal of Evolutionary Biology, 15 (3), 356-361 DOI: 10.1046/j.1420-9101.2002.00410.x

W. Wesołowska T. Wesołowski (2014). Do Leucochloridium sporocysts manipulate the behaviour of their snail hosts? Journal of Zoology , 292 (3), 151-155 : 10.1111/jzo.12094