An Image of Toxoplasma gondii
Zombies have become a pop culture staple in recent years, to the point where you can’t even watch a run of commercials without seeing their moaning, rotted visages. In most modern zombie lore, the zombie affliction comes not at the hands of some voodoo shaman but rather as a result of an infectious agent of some sort (there’s some argument among zombie aficionados as to whether such “zombies” are truly zombies, or if they’re technically “infected”. To me the distinction is irrelevant when a bunch of cannibalistic freaks are knocking down my door howling for brains, but I digress).
Now it may seem that an infectious agent capable of converting average people into roving bands of cannibals might be merely the dreams of folks with one or more personality disorders. And that is true, to some extent – no known agent chemical or otherwise could result in the sort of behavior we see amongst the infected in a zombie movie. However, that doesn’t mean that there aren’t infections that can change how animals behave. In fact, in recent years science has found parasites that make all sorts of different critters do odd things, from zombie ants to suicidal snails.
But those are insects (and mollusks…I’m a biology major so I’m anal about classification :P). Certainly there is no such agent that could modify human behavior? Well…yes. And no.
You see, the jury is still out on how much this little bug (well, protist) affects the human brain. Toxoplasma gondii is a parasite that infects many species of warm blooded animals, including birds, cats, rats, pigs, and humans. Like most parasites, T. gondii has a complex life cycle that involves multiple stages of life and multiple hosts, but for the sake of brevity I’ll stick to the Cliff’s Notes version (do people even use Cliff’s Notes anymore? Or am I just getting old?)
Brain parasite vectors have never been so cute! :D
Anyway. Cats are the primary host for T. gondii, where they engage in the sexual part of their life cycle. Specifically, they reproduce in the cat’s digestive tract. Their young are expelled in the cat’s feces, and it is through contact with said feces that intermediate hosts (including humans) become infected.
The primary intermediate hosts for T. gondii are rats and mice, and it is in these rodents that we can see the frightening brain warping powers of the parasite most clearly. As you might guess, it’s generally in a rat or mouse’ best interest to avoid a cat. However, by means that are not entirely understood, T. gondii can make its rat carrier suicidally attracted to cat scent. When the obvious outcome of the rat/cat run in are complete, T. gondii hitches a ride into the cat’s intestines via the infected rat meat and thus its life cycle is complete.
But let’s back up a minute. I said earlier that humans were an intermediate host for T. gondii, and that one of the primary means of parasite transmission to intermediates is through contact with cat fecal matter. For humans, that mainly occurs when we clean the fuzzy little tyrants’ litter boxes – we breath in microscopic fragments of poo that contain T. gondii cysts. From our mucal membranes the critters make their way into our bloodstreams and eventually into our brain and muscle tissue.
So there you go – cat owners are all infected with a brain parasite that makes mice and rats suicidal (is it any wonder dog owners think we’re nuts?) It isn’t only cat owners though – approximately half the world’s population is infected with T. gondii. Most infections in lesser developed countries come from infected pork as opposed to inhaled cat crap fragments – a much more appetizing avenue of infection by anyone’s estimation!
So…great. We have about 3.5 billion people (give or take) infected with a brain parasite. If that’s the case, then why aren’t we infected gnawing on all you uninfected folk’s marrow by this point? Or at the very least why aren’t we all throwing ourselves at cats in order for them to gnaw on our tasty brains?
Well, it turns out that, unless you have a compromised immune system or you’re a fetus, you aren’t in much danger from T. gondii infection. The initial symptoms at the onset of infection are flu-like, and once those subside the infection is mostly asymptomatic. Interestingly enough though, there are some behavioral changes suspected in infected individuals, but hard evidence of a causal link has been lacking (hence my whole “yes and no” stance earlier in the post).
Apocalypse is off guys! You can all head home!
Researchers suspect that those infected with T. gondii might be more prone to schizophrenia or schizophrenia like symptoms. There are also some links to depression and anxiety. However, it’s hard to tell as no studies have been done involving individuals pre-infection and post infection, given that the scientific community generally frowns on deliberately infecting people with brain parasites.
So, zombiephobes can breathe a sigh of relief – the crazy cat lady down the street isn’t going to wig out because cat poo-borne brain parasites gave her a thirst for warm flesh. And you don’t have to throw Colonel Fluffernutter out to the wolves either (which would be a useless gesture anyway seeing as you’re probably already infected). If there ever will be an actual, honest-to-God zombie pathogen, it’s not likely it will be Toxoplasma gondii.
Andrew Kincaid writes horror, blogs, and watches way too many scary movies.. He’s making the world a stranger place, one story at a time. Get in touch with him on Facebook and Twitter, and check out his debut horror anthology ON DARK PATHS, available on Kindle!
