Friday Weird Science: HALLOWEEN MAD SCIENCE EDITION. The Zombiefying Parasite!

Oct 29 2010 Published by under Friday Weird Science, Uncategorized


I'm always a little disappointed when Halloween falls on such a prosaic night as a Sunday night. Also, in this new, urban environment, I'll admit I don't have the first idea of how to handle trick or treaters.

So you are getting Halloween TODAY!

Here, Sci got you candy!

(The full size bars were always the very sought after thing when I was a kid)

And now, your ZOMBIE PARASITE:

No no, not the kitten. It's IN the kitten. Berdoy, Webster, and MacDonald, "Fatal attraction in rats infected with Toxoplasma gondii." Proceedings of the Biological Academy of Sciences, 2000.

The story I will regale you with today is the classic story of Toxoplasmosa gondii, a protozoan parasite with a truly odd lifecycle. The life cycle requires three things of interest:

1) A kitten
2) Feces. Sh*t. Poop. Crap. Etc.
3) Another mammal. Like a rat.

First, let's introduce you to the parasite:

(Via wikipedia)

Pretty, huh? Toxoplasmosa gondii, meet reader. Reader, meet Toxoplasmosa gondii. I hope you get along!

So this parasite has an interesting life cycle.

(Also via Wikipedia, and I hope it doesn't take over the screen, but it's good to see in detail)

So the life cycle goes like this:
1) A bradyzooite gets eaten by a cat.
2) In the cat's body, the cysts differentiate into sexual gametes.
3) The sexual gametes then combine with each other and share some DNA, dirty style.
4) These gametes mature into an oocyst that is released with the feces.
5) That feces is then ingested by something ELSE (let's say a rat).
6) There, the oocyst differentiates into tachyzooites.
7) The tachyzooites invade the rat's tissues, making MORE tachyzooites.
8) The tachyzooites then differentiate into bradyzooites in various tissues.
9) The rat is eaten by a cat.

Not so difficult. Except for that one thing. "The rat gets eaten by a cat". I mean, rats don't LIKE cats. They usually avoid them at all costs. You might find that understandable. In fact, rats are SO scared of cats that cat urine is used in fear conditioning in behavior tests. Nothing makes a rat freeze up, and look to get the heck out, quite like the smell of a furry feline.

Or at least, these rats avoid cats at all costs...until they eat a toxoplasmosa...

Here's the thing, a parasite can (and does) alter the behavior of an animal for its own benefit. In this case, its own benefit would mean...making sure the parasite can get back to a cat. So how does that come about?


See, that parasite has gotten into the brain, TAKING IT OVER. And when it gets into the brain, it changes the rat's behavior. The first thing observed was increased activity, and a decrease in neophobia (the fear of something new, rats have a very healthy fear of something new, you would too if things liked to eat you, and if the things you liked to eat weren't necessarily good for you, and if you didn't have a gag reflex). But what was REALLY cool was when they put the rats into a cage with some cat urine smell.

You can see above the rat's visits made toward a specific area of an outdoor pen over the course of the night. The rat had four quadrants to choose from: one that smelled like him, one that smelled like nothing, one that smelled like a rabbit, and one that smelled like a cat. Not surprisingly, all the rats spent a lot of time in the quadrant that smelled like them (smells like home!). The uninfected rats spent a lot less time in the other quadrants, and particularly spent less time in the quadrant with the cat odor. The INFECTED rats, on the other hand, spent almost as much time in the cat quadrant as they did in their own!

You can see here a breakdown (with awesome graphics) of preference for two paired chambers in toxoplasmosa infected rats. Over time, they spent less time in the harmless chamber (the one with the rat), and MORE time in the harmful one!! It's not just a lack of cat aversion, it's total cat LOVE.

(That's right, dinner, I'm just washing you up first, it's totally fine...)

The parasite is changing the rat's behavior, by getting into the brain, and making the rat WANT to be around cats!!! Crazy, yes?! It's MAD!!!! INSANE!!! A ZOMBIE RAT who longer has any choice in the matter.

THAT'S some weird science. Even more interesting is that apparently toxoplasmosa happens in HUMANS as well, and studies are ongoing about possible effects in things like schizophrenia (I'll have to post on that later).

But in the meantime, Rats, don't listen to that parasite! Stay away from the cats! Unless it's mine...

I think we all agree that cat couldn't catch ANYTHING.

Berdoy, M., Webster, J., & Macdonald, D. (2000). Fatal attraction in rats infected with Toxoplasma gondii Proceedings of the Royal Society B: Biological Sciences, 267 (1452), 1591-1594 DOI: 10.1098/rspb.2000.1182

2 responses so far

  • Zuska says:

    OMG that is the cutest parasite EVER! Are those little yellow slippers it's wearing?

    That was the most fun science I've read in a long time. Also, Sci-cat is fetching. In the sense of lovely. Sci-cat does not look like Sci-cat would actually fetch, if one were so foolish as to suggest it.

    Great post! ZOMBIE RATS!!!! Who knew????

  • theshortearedowl says:

    Oooh candy! And zombies! And cats! All in the same post! Scicurious wins the internet!

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