Wednesday, October 04, 2006

Parasites That Control Behavior

Sometimes real science is stranger than fiction. Stanford Professor Robert Sapolsky describes a number of examples of parasites or infectious microbes that modify behavior in a Scientific American review article titled "Bugs in the Brain" (pdf)*. Some examples from the review and recent scientific literature:

• The rabies virus increases saliva production and makes the infected host aggressive. When a rabid animal bites a host the virus is spread via saliva in the wound.

Toxiplasma gondii causes infected rodents to specifically lose their inborn aversion to cat pheromones. This behavior is beneficial to toxiplasma, because it sexually reproduces in cats that have eaten infected mice and rats (original article). Infected cats in turn spread toxiplasma through their droppings. People infected with toxiplasma also exhibit behavioral changes, particularly a decrease in "novelty seeking". It's been proposed that toxiplasma infection has actually changed human culture, since there is a correlation between countries with a high rate of toxiplasma infection and increased neuroticism, uncertainty avoidance, and "masculine" sex roles.

• Grasshoppers infected with the hairworm (Spinochordodes tellinii become more likely to jump into water where the hair worm reproduces. The parasite essentially makes its host suicidal to further its own reproduction.

• Some trematodes that infect the brackish water crustacean, gammaridean anthropod cause changes in behavior that make the hosts more likely to move towards light and exhibit aberrant "suicidal" evasive behaviors. These behavioral changes make the infected crustacean more likely to be eaten by birds, which the trematode uses as a host for the next stage in its life cycle (pdf).

• Plasmodium, the cause of malaria, affects both its mosquito and animal hosts. Mosquitoes that drink plasmodium-infected blood initially become more cautious about finding another victim, giving plasmodium time to replicate. Once the plasmodium is infective, mosquitoes become more likely to bite more than one person in a night, and spend more time drinking blood. In turn, once a person is infected with plasmodium, he become more attractive to mosquitoes, continuing the life cycle of the parasite. (See "Malaria Parasite Makes You More Attractive (To Parasites)" New York Times, August 9, 2005). Plasmodium can also affect the nervous system. Infection of juvenile canaries with plasmodium affects the song control pathway in the brain, resulting in simpler songs as adults. (Pubmed).

Of course this research is fertile ground for science fiction. Parasites are often used as a crude form of brain control; the brain-controlling parasites in The Wrath of Khan or the brain slugs in Futurama, are examples of this.

Personally, I prefer microbes with more subtle and interesting behavioral effects. An example of such a story is David Brin's, "The Giving Plague", in which a virus that causes altruism infects the human population. You can read "The Giving Plague" on David Brin's web site.

What other influences might parasites and microbes have had on the human species? For speculation on the possible effects of retrovirus infection on human evolution, see Couturnix's musings on Greg Bear's Darwin's Radio and Darwin's Children, asking "Did a virus make you smart?".

The possibilities are really endless.

* For a more technical review, see Thomas et al. "Parasitic manipulation: where are we and where should we go?" Beav. Proc. 68: 185-199 (2005) (pdf)

(For cool photos, check out the CDC's parasite image library.)

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32 comments:

coturnix said...

Hi - great blog. You may find this about malaria interesting. And you may find this list of essential science fiction interesting because much of it is "biological" SF.

Peggy said...

Thanks for the links. That photo of the mosquito sucking blood makes me itch just looking at it!

Paul Riddell said...

I'd like to add another bit of essential reading: Octavia Butler's novel Clay's Ark was twenty years ahead of its time when it came out, mostly because it works with the same exact material. In this case, the parasite is a virus contracted by the first human expedition to Alpha Centauri, and not only does it give the host compulsions to spread it, the virus also mutates the host's children as well. It's a damn sight better than most SF on similar subjects, and it also has a realistic ending as to what would happen if one vector managed to escape to the outside.

Peggy said...

Thanks for the suggestion Paul. I'm adding Clay's Ark on my "to read" list.

Alice said...

My favorite example of parasites inducing behavioral changes in hosts is the fungus _Entomophthora_ ("insect destroyer"). When it infects flies, they engage in mating behavior (thus spreading spores to new hosts) and seek out high places (which also aids in dispersal).

profnasty said...

Web MD saysa toxoplaswatever cures itself. Once infected and cured by natural defenses, antibodies prevent renewed infection. Let's don't everybody fly off the handle on this one people.

jerry said...

Try MMS www.miraclemineral.org

It's effective with malaria and AIDS.

It's also very effective with sinusitis from personal experience.

Anonymous said...

there is a parisite that murders millions of humans its called capitalism.

Anonymous said...

People who have never read Carlos Castaneda books should!! Especially his last one--THE ACTIVE SIDE OF INFINITY. They are called--'the flyers'.
It is the parasites that control us for their food. Our egos are the byproduct of this organism. We feed our ego therefore we feed it. Its all very simple. This effecient parasite is not physical. You cant remove it with your hands or technology. The only way to overcome it is to let go of every preconceived idea you have ever had!! Easy huh?

Anonymous said...
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Anonymous said...

The Toxoplasmosis effect referred to by WebMD I think isn't the lesser known possible behaviour modification. But instead the whatever toxic infection it gives to pregnant women and infants. That warning on the back of the kitty litter box doesn't say "Warning, pregnant women may love their kitties even MORE!!!" They're referring to possible life threatening illness, so I don't think the brain parasite quite cures itself.

Jane Carter said...

What is completely missing is an explanation of how such behaviour could have evolved. I work at a hotel in Prague The Castle Steps Hotel, Prague. It is hard enough to get staff to do what they are told!

Seriously, however, how could such behaviour develop step-by-step, with each stage being a result of a genetic mutation? It is hard enough to envision a genetic mutation which causes a useful change in an individual species. In this case, the mutations would have to cause a change in the parasite which then led to a useful change in its host. This is fine if the parasite is simply turning up or down a piece of existing behaviour. However, in some cases the behaviour is entirely new.

Grimjack said...

Cat people are definately different from dog people. But i dunno about that novelty seeking bit, i think it may just make them more doting on their cats. Most cat people I know are more introverted, and the novelty in life they seek are more inward than outward. Like new life modalities over new physical adventures. It makes them less likely to commit dangerous acts that might interfere with the flow of catnip. Because the catnip must flow!!

Grimjack said...

Should we expect a darwin's cheatlist of how toxoplasmosis effects particular human traits? Or just look at the overall effect, this early in the game. Its a new theory to me, so I'm not expecting us to know everything. In fact I'd expect the majority of science to know nothing, on this particular subject.

The parasite could be manipulating inlaid child rearing behaviours. Those are already in place, and how many cat people have you seen refer to their cats as their babies? Parenthood makes people more likely to slow down in life. To settle down and work on raising their children.

If you wanted a paper that detailed, you better get ready to read a book. After a century of research. I'm not quite ready to dismiss this theory because every dot isn't yet connected.

Dr.Deadhorse said...

"The catnip must flow!"

Bwahahaha! Good one!

He who controls the catnip, controls the universe!

And don't forget Heinlein's The Puppet Masters which is a pretty creepy book about parasites controlling their hosts.

rocketdev said...

Dr. James Boudreau discovered a connection between the micro and the macro world in the 70's. He was researching olfaction and gustation. he also mapped the feline brain as part of his studies.
His epiphany from that work was so profound (the idea that micorganisms affect human behavior) that he divested himself of his material possessions and became a budhist monk!

Peggy said...

Alice: Entomophthora make a great addition to the cool parasites list.

profnasty: I'm not sure what you read, because WebM D does not say toxoplasmosis just "cures itself". It just says that the symptoms remain "subclinical", meaning that you can't obviously tell you are infected.

jerry: Malaria, AIDS and sinusitus? It must be a miracle. Perhaps if you dilute the miracle mineral in water enough times such that there are no molecules of it left, it would be even more effective!

Note to spammers: I may leave your comment up to mock you, as long as the link isn't live.

Peggy said...

Anonymous: I didn't know Carlos Castaneda wrote about things other than his peyote trips.

Jane: there has been a lot of work on the co-evolution of parasites and their hosts. All you need is some variation in the parasite population. A small fraction of the parasites infect a part of the brain or release a compound that affects the host's behavior. If the change in the host's behavior makes it more likely that the parasite's offspring will be passed on to a new host, that particular behavior-changing variation will be found in an larger portion of the parasite population. If toxoplasma does change the behavior of humans (and that idea is controversial), it would probably be too subtle to notice without a test.

Peggy said...

Grimjack: so do you think people who are drawn to cats are naturally less novelty seeking or is it interaction with cats that causes that personality type?

Dr. Deadhorse: The Puppet Masters is another good sci-fi example. It seems to be a popular theme!

Rocketdev: That's an interesting story. I wonder why he decided to become a monk rather than pursue his research?

Anonymous said...

Ever wonder what else is in those chemtrails besides metal salts for wave guide weather mod applications? Could it be fungal/parasitic/viral/prion manipulation of our psychobiological existence and evolution. Welcome to a world of protien economics and disaster capitalism. WHat is this emerging condition called morgellons just recently covered by MSM? Just wondering! Could be all quite different than imagined, yet if one imagines enough, some hypothesis are likely to be correct. One thing is clear, we've officially, globally, entered a Brave New World scenario. Search "Sentient Parallel Word" to get a drift of the direction of our world. Is it control just because they can (and $), or are there bigger reasons? With RNI (both visual and auditory), psychoenergetic manipulation of the unconscious process, RHIC-EDOM, bioenergetics, geo/weather engineering, to name a few, well, "Welcome to the Jungle." I suspect it's all much more complicated than that which is proposed above. If only I had a Scully by my side. That's unlikely; private journey's to dark places. Hi guys. Yours Truly, and Forced Regards, Anonymous.

Slipton Fell said...

It's easy even for a non-scientist to see how parasites can affect human behavior. Just look what politicians have done to the world.

Jason Carpenter said...

The video game Resident Evil 4 features a creature called "Las Plagas," which is an alien parasite that controls a human host. An interesting fact: to make the game more realistic, one of the characters refers to some of the real-life parasites listed in this article as proof that something like Las Plagas could actually exist

rocketdev said...

I don't have an answer for Peggy about my friend becoming a monk. It may have been related to God and Microorganisms (seems so).

Morgellons may be a test to determine if high tensile fibers can be grown in humans (only partly sarcastic).

The natural selection of parasites would also apply to the hosts. So we must be well adapted to accept the benevolent chemical signals of our myriad interior inhabitants.

The malevolent signals though are puzzling. Are they meant to create more food for the necrophiliae amongst the micro's?

Paul Mohr said...

I know this is silly but my mind has it's own regulatory system and it seems to be off today. Do politicians fit in the class of parasites that control behavior?

Benjamin Rosenbaum said...

Scott Westerfield's Peeps is also full of behavior-controlling parasites!

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RL said...

Nice article!

Re: Resident Evil 4...

The fictional "Los Plagas" mentioned was not alien, but actually an ancient inter-specie parasite "discovered" in an underground mine.

Below were the other organisms mentioned (with their texts) as cited in http://www.capcom-central.com/ResidentEvil/re4.php?page=files3

Diciocoelium - Once the larvae of this parasite migrates to the ant's esophagus, it alters the behavior of the ant. When the temperature drops in the evening, the infected ant climbs to the top of a plant and clamps onto a leaf using its mandible. It stays there immobile until the next morning, placing the ant where it's most vulnerable to be eaten by a browsing herbivore such as sheep. One could conclude that the parasite is manipulating the host's behavior to make its way into the body of its definitive host.

Galactosomum - The larvae of this parasite makes its home inside the brain of a fish such as the yellowtail and the parrot bass. Once infected, the fish make their way up to the water's surface, where they'll swim until being eaten by seabirds. Once again, this peculiar behavior can only be explained by the parasite's desire to get into the bodies of the seabirds.

Leucochloridium - This parasite's sporocysts develop in the snail's tentacles. The spororcysts are vivid in color and pulsates continuously somewhat like a worm. Suprisingly, the infected snail makes its way to the top of a plant where it is more visible to the eyes of birds. Therefore more likely to be eaten. Once eaten by a bird, the parasite will complete its metamorphosis into an adult.

RL said...

Nice article!

Re: Resident Evil 4...

The fictional "Los Plagas" mentioned was not alien, but actually an ancient inter-specie parasite "discovered" in an underground mine.

Below were the other organisms mentioned (with their texts) as cited in http://www.capcom-central.com/ResidentEvil/re4.php?page=files3

Diciocoelium - Once the larvae of this parasite migrates to the ant's esophagus, it alters the behavior of the ant. When the temperature drops in the evening, the infected ant climbs to the top of a plant and clamps onto a leaf using its mandible. It stays there immobile until the next morning, placing the ant where it's most vulnerable to be eaten by a browsing herbivore such as sheep. One could conclude that the parasite is manipulating the host's behavior to make its way into the body of its definitive host.

Galactosomum - The larvae of this parasite makes its home inside the brain of a fish such as the yellowtail and the parrot bass. Once infected, the fish make their way up to the water's surface, where they'll swim until being eaten by seabirds. Once again, this peculiar behavior can only be explained by the parasite's desire to get into the bodies of the seabirds.

Leucochloridium - This parasite's sporocysts develop in the snail's tentacles. The spororcysts are vivid in color and pulsates continuously somewhat like a worm. Suprisingly, the infected snail makes its way to the top of a plant where it is more visible to the eyes of birds. Therefore more likely to be eaten. Once eaten by a bird, the parasite will complete its metamorphosis into an adult.

Austin B. Blevins said...

Hey, just something to think about and I may be a retard for saying this, but I took a look at "the giving parasite" or at least I think that's the name by David brin and the concept of the parasite that makes you a better person is amazing, but what if that was just a ploy to get into our skin, perhaps these parasites are geniuses with a brain much like that if a bee of a hive or ant of an anthill were all of the parasites think as one and are being nice until using their intelligence they find their way into every human and or possibly animal when they will start to attack, either by killing us or by taking complete control just like the Los plagas took control of the humans in resident evil 4, I know this is insane and retarded, but isn't the concept alone something interesting to think about?

Peggy said...

Austin: I'm pretty sure you are thinking of is David Brin's "The Giving Plague" where the culprit is a virus, not a parasite.

You can read it for free on Brin's web site: The Giving Plague

Evilsniper626 said...

ZOMBIE APOCALYPSE!!! >:D

Annie Newcombe said...

Earlier studies showed that mice lose their fear of cat urine for a few weeks after infection; Ingram showed that the three most common strains of Toxoplasma Gondi make mice less fearful of cats for at least four months. I hope doctors could find solution for these especially to human infections.