Mind Control By Parasites
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Basic Information

February 10, 2006: Article discusses the link between parasitism and self-destructive behavior. There are parasites that provoke specific suicidal behavior in animals, so as to spread the parasite to other organisms.

  • Half the world's population (of humans) is infected with toxoplasma gondii.
    • In rats, this parasite overrides their fear of cats and cat urine.
      • In some cases, it makes them seek out cats.
      • This is because the parasite has to go through part of it's life cycle in cat intestines. So it tricks rats into making themselves easy targets.
    • Children born to human females with toxoplasma gondii infections are more likely to develop schizophrenia.
    • In both rats and humans, t. gondii can be treated with either pyrimethamine, an antibiotic that kills the parasite (and also cures malaria), or with Haloperidol, an antipsychotic. Both appear to provide relief from schizophrenia, and both restore rats instinctive fears of cats.
  • Other parasites mentioned include:

June 22, 2021: Further evidence that t. gondii increases risk taking behaviour in hyenas.

See Also:

Zombie caterpillars controlled by voodoo wasps


3. related SciShow Video about Mind-Controlling Parasites.

Game and Story Use

  • Any of the above would be a good scientific grounding for a zombie virus. Zombies seek to infect new hosts, because the virus or fluke in their undead brains wants to spread.
    • Pick (cat and rat), (ant and cow), (fish and bird), or (grasshopper). Zombie versions of the chosen animals exist, and can spread the infection as easily as a brain-eating ghoul. As if mundane zombies weren't bad enough, now you have to beware of zombie cattle herds, or rabid fish.
  • No one really likes cats. They're evil little furballs. It's the T. gondii in our systems that compells us to feed and shelter them, so that more parasites can spread. Eventually, everyone will be infected, and then it'll be an entire world of crazy cat ladies. :)
    • Perhaps this is the true story behind Lovecraft's The Cats of Ulthar.
    • Would make a cool planet of hats - a world where everyone loves some vile pet, but it's because of a brain fluke. At first the PCs can't stand the things, but once you fail a saving throw, you find you love them, and want to take a few pets back to federation headquarters with you. No sinister plan involved, the only bit of free will being subverted here is forced love of an ugly pet. This gets into some tricky gray area, with no certain right or wrong action - you don't want to kill people's pets, but you don't want the infection to spread. And while most people think the critters are ugly before they get infected, even if the parasite is killed, the ugly pets will have no doubt grown on a few people.
  • This reveals the true nature of the "special bond" between wizard and familiar - magic is a parasite that lives part of it's life in the brains of spellcasters, and part of it's life in the gut of cats.
    • Perhaps when a wizard dies, his familiar consumes the corpse.
    • A Displacer Beast might just be a genetic mutant - a cat that's evolved to be a carrier and full-life host for the magic fluke. It no longer has a need for wizards. If it bites a normal cat, they'll become a displacer beast, as well. Or similar pseudoscientified nonsense. Heck, maybe those big tentacles on it's back are just late-stage parasite flukes.
  • A parasite that lives part-time in vampires or some other supernatural predator might drive humans to seek them out1. Puts the paranormal romance genre into a different light, doesn't it?
  • The next question is, how does t. gondii benefit from making humans schizophrenic?
    • There is some suggestion that it is part of spectrum of increased risk taking behaviour including greater sexual promiscuity and violence … it may be adaptive for the parasite, perhaps increasing transmission opportunities, or it may be a maladaptive side effect of being in a species that it is not fully adapted to being hosted by.
  • Presumably a hyena that isn't scared of lions isn't going to avoid humans either … and thus is more likely to wander into camps and settlements and end up biting someone.
  • How about a parasite that actually upgrades the host's mental faculties - more of a symbiote in fact? The upgrade could be from the symbiote subverting the hosts and using its own intellect, or might upgrade the host directly: regardless, given time and selective advantage, we might find the two evolving together to form a sort of composite species.
    • Lore from "that RPG" suggests that their iconic "mind flayers" had developed from humans in this manner - and (at least in the "current" era) were still obliged to reproduce by installing a "tadpole" into a wild type human, where it consumed and replaced the entire CNS above the hindbrain and then transformed the body for its convenience.
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