Endemic! Week: Brain Parasites

Endemic! Week: an entire week of microfiction crafted around the word “endemic.” If you missed the introduction, read about it here.

They Always Land on their Feet

“Brain parasite Toxoplasma gondii infects rats through cat feces. It reprograms the rats’ brains. Make them fearless thrill-seekers,” Erica shouted over the plane engine. “They’ll dance between a cat’s paws after infection. Cats give people Toxo too. Freaky, eh?”

“Not really. Imagine losing your fear of death–sounds exhilarating. The ultimate adrenaline high,” Dave answered.

“Suit yourself. See you at the bottom!” Erica leapt from the plane’s open door. Far below, Erica’s parachute unfurled.

Dave gazed at the mountain peaks below. Like fang-rimmed jaws. “I’m going now!” He jumped.

The skydiving instructor grabbed for him, missed. “Wait! You forgot your ‘chute!”


Hard at work producing brain parasites.
Hard at work producing brain parasites. (Photo credit: Wikipedia)

Do you own cats? Then there’s a chance that you’re already infected with toxoplasma gondii. The bad news is that Toxo is endemic among people who clean cat litter boxes, eat raw or undercooked meat, or eat unwashed veg. The good news? Provided you’re not pregnant or immunocompromised, Toxo appears to be relatively harmless.

Toxo’s a versatile protozoan (not the same thing as a bacterium or virus). All felines, from housecats to tigers, act as its primary host. Inside the intestines of cats, Toxo undergoes sexual reproduction and forms packages called oocysts in the intestinal lining. These oocysts, filled with dormant Toxo cells, get shed when the cat poops.

Next, the oocysts lie in wait for another warm-blooded mammal to stop by the cat scat. Someone like Dave, perhaps, scoops out the litter box, forgets to wash his hands, and with his next meal he consumes a few oocysts. When those oocysts hit his intestines, they spring into action, infiltrating the intestinal lining, but this time their goal is to release invaders directly into the bloodstream. These bits of Toxo ride your blood all over your body, setting up shop in your organs, muscles, and brain.

Yes, it infects your brain.

Life cycle of Toxoplasma gondii
Life cycle of Toxoplasma gondii. (Photo credit: Wikipedia)

The Toxo forms cysts in the areas it settles in, and congratulations: you’re now permanently infected with Toxoplasma gondii. You’ve got ’em for life, buddy. Fortunately, this is as far as the Toxo can go. It just hangs out, hoping you’ll get eaten by a cat so that the whole cycle can start anew.

Unfortunately for Toxo, humans don’t get eaten much by felines these days. Perhaps we featured more prominently in Toxo’s life cycle back when lions and bobcats were a daily threat. Nowadays, it’s mice and rats that primarily perpetuate the Toxo cycle.

Here’s the interesting thing: in rodents, Toxo infection causes behavioral changes. Rats with Toxo lose their fear of cats. They’ll attack cats directly, or just waffle around when a cat comes after them. Obviously this is to the Toxo’s advantage — it wants the rat to behave dumbly so it can get eaten by a cat, continuing the life cycle. There’s evidence that Toxo causes personality changes in humans as well, making us more likely to take risks.

How common is Toxoplasma gondii? It’s one of the most common parasites found in humans. Up to a third of the world’s estimated to be infected. If you live in the United States, your odds are one in four. So wash your hands, wash your vegetables, and don’t eat cat poop. Otherwise you’ll join the standing army of Toxo carriers all around us right now.

3 thoughts on “Endemic! Week: Brain Parasites

  1. Good news for cat owners: house cats are less likely to become carriers; it’s more of an outdoor cat concern since those are the felines most likely eating infected rodents. If there are no mouses in your houses and Mittens dines on “feasts most fancy” and “vittles most tender,” then she’s probably not sharing brain parasites with you. The other cool thing is that the risk for pregnant women only comes if her initial infection with T. gondii comes /during/ pregnancy when the immune system is already having a minor freakout. If the woman is already a carrier when she becomes pregnant, then there’s no risk if mom decides to clean the litter box. More infections are believed to come from food, though, (especially through eating undercooked pork or lamb) and different countries show different infection rates, often tied to socioeconomic conditions and endemic cuisine (Ha! See what I did there?). I tried to find a publication relating specific dishes to infections instead of something that made generic claims about food preparation, various countries, and local cuisine, but instead stumbled across a different scary thought: a recent publication suggests that the recent trend towards free-range and organic also produces meat with a greater T. gondii risk. So, saving the earth now comes with bonus brain parasites! (Foodborne toxoplasmosis. Jones JL, Dubey JP. Clin Infect Dis. 2012 Sep;55(6):845-51. doi: 10.1093/cid/cis508. Epub 2012 May 22. Review.)

    1. Thanks so much for all the awesome additions and clarifications! I’m feeling much less smug about my lack of cat ownership and much more afraid of that delicious organic chicken in my fridge.

      New plan: I for one welcome our new brain parasite overlords! Do you think this is how Hypnotoad got his start?

  2. Very real possibility! I also hear that worms are supposed to be good for you; they rewire your neurons in beneficial ways, jazzercise your muscles, and make general overall improvements.

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