Crazy Cat Ladies; is there something to it?

The parasite T. gondii, seen here, may be changing connections between our neurones, altering how we act and feel. (Dennis Kunkel Microscropy, Inc./Visuals Unlimited/Corbis Images)

My colleague in Biology, Dr. Bruce Smith, brought me a microbiology story that he thought I might enjoy, via The Atlantic Monthly.  His comments to me as he handed me this article printout were

…that magazine is way too liberal for me, but I thought you might like it…

Spot on, Professor Smith, I do like The Atlantic! Thanks for bringing this to my attention, and this is only the second posting where I let my political leanings out (here is the first one ever, and I still think Michelle Bachmann is unfit for office.)

The news article recounts the ongoing research of Dr. Jaroslav Flegr, from Charles University, Prague, Czech Republic, who has proposed that the protozoan parasite Toxoplasma gondii has developed a mechanism for manipulating the behavior of the hosts that it infects.  Toxoplasma infections are not new; there is a wide body of medical literature describing the significant effects of the parasite on the developing fetus, and outlining the route of transmission from cat feces into humans. This risk is why I am still changing the litterbox in our house 13 years after the birth of our last child, however I suspect that the risk to the women in the house is significantly diminished currently.

Flegr began by recruiting college students for behavioral tests, and testing them for the presence of Toxoplasma. Infections in the Czech Republic are endemic, with upwards of 30 to 40% of the population having a latent form of the disease. What he concluded after examining large numbers of subjects was that many patients had delayed reaction times in tests, and overall personality types fell into distinct groups. Males with the parasite were typically more “introverted, suspicious, [and] oblivious to other’s opinions” in comparison to uninfected individuals, however females with the parasite were typically much more outgoing and trusting than uninfected women. Flegr continued his studies and found highly reproducible results in civilian and military populations as well.

The behavioral studies conducted by Flegr are intriguing, but without a neurological mechanism to explain them, they at best demonstrate a correlation between an infectious agent and human behavior. What is missing is experimental evidence to show causality between Toxoplasma and these behaviors. Animal models are the solution to this problem, and a number of studies have now been conducted which examine the effects of behavior modification of rodents following Toxoplasma infection. Joanne Webster, of Imperial College London, has show that infected rats are more active and less cautious than uninfected rats. Examination of the brains of infected rats showed that metabolism of the neurotransmitter dopamine was altered in these rats, and that anti-dopaminergic drugs could suppress the observed behavior changes.  One additional finding was highly intriguing; when infected rats were put into large cages with defined areas of cat urine, the rats actively sought out and remained at the areas with the cat urine, indicating that the behavioral changes in the rats were making the rats seek out cats and enabling the parasite to return to its definitive host. This has become known as “Fatal Feline Attraction.”

The interview in the Atlantic article concludes with more material from Prof. Flegr, who has recently completed a behavioral study in humans, supporting Fatal Feline Attraction in humans.  In a blinded study, he found that infected men like the smell of cat urine, while infected females have the reverse response towards cat urine. Control urine samples included dog, horse, hyena, and tiger(!), and infection had no effect on how those samples were rated. So I’m guessing the reason I am still changing the litterboxes is because I have a latent infection with Toxoplasma, as does my wife who cannot stand the smell of the boxes. Mystery solved!


About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on February 15, 2012, in Strange but True, Yikes!. Bookmark the permalink. 9 Comments.

  1. Wow that is fascinating! I had heard that pregnant women should not change the litter box, but I never knew until I read this that it was because of a parasite. It made me wonder if the latent parasite could still harm a fetus, and I discovered upon a little research that it usually does not unless infection reoccurs due to immunodeficiency. I also learned that infection has worse effects on young children, so its probably best to keep them away from the litter box, too.
    What I found especially interesting about your blog post was the fact that men who are infected like the smell of cat urine. It certainly helps explain why this one man I know doesn’t seem to notice how awful his house with four elderly cats smells.

    • Jess, you get a “thumbs-up” for the last part of that comment. My spouse also doesn’t understand why I put off changing the litterbox until it reeks, but it just doesn’t bother me as much. I can now comfortably claim “the toxoplasmosis made me do it” when I say the box doesn’t need to be changed.

      I had heard of the rat/cat link before, but hadn’t heard of those kinds of behavior alterations being extended to humans. The article linked to in the Atlantic Monthly includes statements that behavior modification in humans due to Toxoplasma might account for tens to hundreds of thousands of deaths annually worldwide. I had heard previously though that infection due to this organism is “considered to be the third leading cause of death attributed to foodborne illness in the United States” (source Centers for Disease Control) however the majority of these fatalities are in immunocompromised (e.g. HIV infected) patients.

  2. I have heard of the toxoplasma having adverse effects on an unborn fetus, but the personality changes that occur in adults who are infected was fascinating. It also explains possibly why I can always smell the litter box before my guy friends. I also heard of the rat/cat link that the Toxoplasma can make a rat less afraid of cats and even friendly with them. The cat will then eat the rat and the Toxoplasma will then be in its preferred host..the cat. I find any organism that can change one’s personality quite fascinating, but I also have an obsession with zombies and what type of organism could actually cause that. I also find it interesting, concerning zombies, that the CDC actually has a preparedness and response plan in place to follow for zombies.

  3. Sweet! Someone picked “tiger” pee in the poll up above. I have to say, I personally would be going in the other direction if I actually smelled tiger pee.

  4. Wow. I’m sorry I missed this post in it’s initial release. In the poll, I voted for cat pee because I used to work for a company whose stock symbol was CATP, which everyone found just hi-friggin-larious. My business partner has a great story involving a tiger, the call of nature and a girl he took to the zoo on a date in college I’ll have to tell you some time. And lastly, I’ve been meaning to get around to watching a documentary on Cat Lady Dementia ( from ’09 but haven’t gotten round to it. I just moved it to the top of my Netflix list. I’ll let you know if there’s any science in there you can work with.

    • Well, from my interpretation of the article above, the traditional “crazy cat lady” is a misnomer. Think about it; Toxoplasma infection in females leads to a strong aversion to cat urine, and presumably would result in someone who shuns cats. It therefore seems to be the men in their lives (who tolerate, and indeed seek out the smell of cat urine) who are the enablers in this situation.

      Aw crap!

  5. “Fatal feline attraction” would be a great band name.
    I have always been the designated cat box cleaner and I don’t mind (not even when the cat watches and waits to dirty it up as soon as there’s fresh litter). Maybe I am just the ultimate cat lady. Or I have no aversion to bodily functions. Probably both.

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