Wednesday, 3 March 2010

calm it down. here, have some toxoplasmosis

yet another infectious disease post :/ i'm sure we're all hanging on the edge of our seats waiting to hear what horrors the microbial world holds for us today.

when i was an undergrad (which seems like ages ago. oh, how old we have become), i recall very distinctly learning of the organism toxoplasma gondii. although the physiology and pathology of said bug is interesting and all (not really, i lie), the thing that captured me the most is the ability for the protozoa to change the nature of its host. here, let me explain:

mice, are naturally afraid of cats. this goes by the observation, but for the more darwinian amongst us, you can easily place mice in canonical evolutionary pressure model: mice that are afraid of cats tend to die less, than those which do (duh) and therefore have a higher chance of reproducing, giving rise to progeny which have (inbuilt) ability to avoid cats. or other horrible predators. anyway, mice are scared of cats. pretty intuitive.

now, toxoplasma is a parasite of mice, amongst other things. and in infecting mice, they make their way to various organs of the host, and of particular interest to us, the brain. there, it effects the host mouse by physically and chemically altering the various nuclei and gyri (for the keen neuroanatomist, 10 points if you can recall which i am talking about), to make mice unafraid of cats. in fact, as my lecturer puts it, the mice frolick and prance around in the sun, basically begging for the cats to come over for dinner. and we all know, what's on the menu. this, in turn, helps the protozoa infect the cat, which happens to be it's definitive host (in which toxoplasma reproduces), and then the cat shits spores out, ready to infect various new hosts, such as other cats, mice, wildboars, pregnant women (of which toxoplasmosis is a particularly nasty disease to the unborn child, but that's another story altogether), stegosauruses, magical leopleurodons and fanciful unicorns.

in a nutshell, the toxoplasma has made mice bolder in order to perpetuate itself. amazing. this is a very awesome example of how a parasite directly influences behaviour, as opposed to only physiology (like giving you a runny nose and making you puke something nasty).

now, take this information and combine it with some newly published paper (remind me to link it, sometime) from czechoslovakia, which shows that toxoplasmosis in humans, may become benign (form spores in your brain, but not actually do anything. gives a new meaning to 'monsters in my head', doesn't it?) but cause us to be:
1. calmer
2. self-depressive
3. more extroverted
4. rebellious
5. more assertive
6. ???
7. profit
8. schizophrenic and who knows what other mental disorders

amongst other things. so. in conclusion. the next time, you feel like you need a little pick me up. or you can't find a pint of beer to give you that much dutch courage to talk to the hot chick down the bar. or you feel like you need to break someone's kneecaps with a sledgehammer. maybe you just need an intravenous injection of purified toxoplasma cysts. oh, yeah.

also, bonus question to add onto that 10 from earlier (you keen little buggers), why is mycobacterium such an oxymoron, myco- being the general prefix for fungi, and -bacterium the suffix for... yeah, you guess. don't cheat by using wikipedia or something like that. for shame.


Anonymous said...

i just hv a patient in ward today investigating for toxoplasmosis...


Nusayb said...

First of all, I think sulci and gyri are a much better pair than nuclei and gyri.

And secondly, I wonder if the changes that occur as a result of toxoplasmosis in humans lead us to become more amenable to having cats in our immediate environment. In other words, are calm, 'self-depressed', extrovert rebels more cat-friendly?

etc said...


oh noes, i hope he was duly subdued, and was extra nice, though.


actually, even though you are right in pointing out the better wording, i have accidentally given away the answer by using the word 'nucleus'.

Nusayb said...

Ah, my bad! I failed to realize the meaning behind the play on words; too focused was I on the form that I forgot to consider the function...