by Emily Berry
My housemate is convinced I am a crazy cat lady and perhaps he is right; I talk to my kitten, Holly, like she’s a person. It’s time I accepted the fact I am going to be one of those older women who refers to her sixteen cats as ‘her babies.’ But, maybe it’s not my fault – maybe there is a reason I adore my cat so much. Maybe I am being brain-washed by a nasty little parasite that loves my cat even more than I do.
Sounds strange, but it’s true. The identity of this cat-loving, mind-controller is Toxoplasma gondii. This single-celled protozoan can infect nearly every bird and mammal but, through all the animals they infect (called their ‘secondary hosts’) there is one special place these protozoans long for. The only place they can reproduce is inside the intestines of cats, their ‘primary hosts’ – and they will try anything within their protozoan power to get there.
They are even capable of altering the behaviour of their secondary hosts in order to increase the chances of being reunited with their precious cats. They perform this mind-control splendidly in rats, reducing the rats feelings of fear and anxiety so they are less likely to avoid cats, and more likely to be eaten by them – pretty clever eh?
How T. gondii has managed to control its hosts remained a mystery until quite recently. It brain-washes its victims by hijacking the very part of them that’s supposed to protect them from nasty little parasites like this – the white blood cells. It infects these immune system cells, giving it direct access to the brain and causes the cells to release GABA (or gamma aminobutyric acid, if you fancy a tongue twister). GABA is a neurotransmitter that, amongst other things, inhibits the sense of fear and anxiety!
Not only does this parasite make rats fearless of their cat-enemies, but studies have shown that infected rats even show signs of being attracted to cats! Not only are they less likely to avoid them, but they are more likely to directly approach these predators – all good news for the T. gondii that is now happily settled in the cat’s stomach.
The ability of this tiny organism to make rats ‘fall in love’ is where my crazy cat lady dilemma comes in. We are also capable of becoming infected. In fact, research estimates that up to 80% of the population may be infected, although most have no idea they are housing this parasite. But, is it responsible for my (some would say) excessive love of cats?
Put simply, the answer is no. There is no science to back this up (which is a shame as I was hoping for an excuse). However, that doesn’t mean we get off scot-free. Many infected people have noted a certain lack of fear. More worryingly, an infected person is more than twice as likely to be in a car accident. And there’s more bad news – scientists have found links between T. gondii infection and the occurrence of depression, schizophrenia and even suicide, although the jury’s still out on whether the parasite is the exact cause.
Questions remain unanswered about the effect of T. gondii on our own minds, but one thing is certain, this incredible parasite will be studied and marvelled for years to come. A single-celled organism that can brain-wash a species as complex as ours – what could be more fascinating than that?
Emily Berry (@lemonyem) is currently studying for a Master’s in Biological Science at the University of Sheffield, UK
Flegr J, Havlícek J, Kodym P, Malý M, & Smahel Z. (2002) Increased risk of traffic accidents in subjects with latent toxoplasmosis: a retrospective case-control study. BMC infectious diseases, 11. PMID: 12095427
Fuks J.M., Arrighi R.B.G., Weidner J.M., Mendu S.K., Jin Z, Wallin R.P.A., Rethi B, Birnir B & Barragan A. (2012) GABAergic signalling is linked to a hypermigratory phenotype in dendritic cells infected by Toxoplasma gondii. PLoS Pathogens, 8 (12). DOI: 10.1371/journal.ppat.1003051
Berdoy M, Webster J.P. & Macdonald D.W.(2000) Fatal attraction in rats infected with Toxoplasma gondii. Proceedings of the Royal Society B-Biological, 267(1452). DOI: 10.1098/rspb.2000.1182