Look, I happen to be stuck – in you.
And it's really all your fault. You must have gotten yourself infected by eating uncooked meat or, if you happen to have a cat you probably got a little too close to its feces – either way, you're gross. Do you remember that flu you had a few weeks ago? That was me. Or rather that was your immune system trying to get rid of me, which by the way – rude! Others of my family have infected about half of your sorry population around the globe and most of them were doing fine, no symptoms whatsoever. The way a host should behave, if I may say so. So now, I am crammed into a cyst with who knows how many of my kind and have to lie around semidormant. I don't know if I will ever see the comfy squishy cells of a cat's intestine again, ergo I don't know if I will ever get to sexually reproduce again. Picture that! Sure, I could keep on merrily dividing in you but then your immune system would probably start going all rampage-y again on me, so no thanks. You are just seriously lacking as an intermediary host.
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| Dividing T. gondii, courtesy of Ke Hu and John M. Murray [1] |
And this is not me whining – I happen to have been through a whole lot of intermediary hosts: mice, rats, once even a cow. I might be a small, arched parasite but I am capable of surviving in just about any warm-blooded animal. And outside of them, too! In fact, I have been told that I am very resilient to cold climates, thank you very much. Plus, in mice and rats I stand at least a fighting chance to get back into a cat. See, I happen to not only be resilient, highly international and wisely adjusting my proliferation rate so that hosts don't kick me out – I can tweak behaviour of animals who are ten thousand times my size. See, I propagate into my inter-host's brain, I fiddle about a little here and a little there, some hypomethylation of genes that are expressed in the amygdala, a bit of histone-lysine acetylation of astrocytes. And voilà: mice lose their fear of cat urine. Rats even find the smell more attractive! They stop avoiding marked territory and they become altogether less capable of escaping the cat they sniffed out. Isn't that just great?
But humans...pesky. There was a time when getting you eaten by a big cat, say a lion, was a real option. But nowadays you have become so cuddled away and safe with your sweet little overfed furballs. I mean, toxoplasma gondii is no quitter, mark my words! A toxoplasma infection is associated with some neat little behavioural changes in humans: Males show higher levels of testosterone, are more likely to disregard rules. Both of your sexes perform worse in respect to reaction time and concentration. We are associated with higher risks for schizophrenia, bipolar disorder, suicide and traffic accidents.
Still, getting out of a human and back into a cat is hard work. I'm a nice little fella, just wanting to get back to my favourite host.
So. About my being stuck – would you care to get eaten by your cat?
Malika Renz
MSc Student, MedNeuro
Want to know more?
[1] Hu et al., PLoS pathog 2006
[2] Webster, Schizophrenia bull, 2007
[3] Flegr, Schizophrenia bull, 2007.
[4] Torrey et al., Schizophr res, 2012
[5] Hurley et al., J neuropsy clin neurosci, 2012
This article won the Best Contribution award for the issue Brain Invasion Thanks Malika for such a fun take on a complicated subject!
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