The science behind “Crazy Cat Ladies”

 

Are you a cat or dog person?

This question is more than just a conversational icebreaker. Your answer may determine whether you’re more or less likely to have get in a car accident, hoard things, develop a mental illness, and succeed in business.

These seemingly unrelated phenomena have something in common: a very clever cat-dependent parasite by the name of Toxoplasma gondii that might just have the powers of mind control.

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The life cycle of toxo & mouse mind control

Toxoplasma gondii (T. gondii, or “toxo,” for short) can multiply in many hosts – humans included. But it can only reproduce sexually in the intestines of cats. After the parasite lays its eggs (called oocytes) in a kitty’s belly, the future parasite babies are then shed in the cat’s poop.

A single cat, in fact, can shed up to 100 million oocytes.

Toxoplasmosis has been most thoroughly studied in mice. That’s because mice have (as they should) a deep-seated, innate fear of cats. When rodents are infected with toxo, however, a strange thing happens: they fear not the feline. In fact, toxo-infected rodents appear to be attracted to cats, displaying more reckless behavior and slower reaction times in the face of danger.

This is wonderful news for cats, who now have dinner delivered to them – minimal sleuthing, hunting, and pouncing required.

Infection with the Toxoplasma gondii parasite is known as “toxoplasmosis.”

After a cat eats a toxo-infected mouse, the toxo cysts in the mouse make their way to the cat’s intestines. Once in they’re in the kitty’s gut, the toxo cysts can once again sexually reproduce to make oocytes, completing the cycle.[1] (Cue: Circle of Life, from the Lion King)

 

 

How does toxo make a timid little mouse prance into the jaws of its predator? It has been suggested that toxo invades a rodent’s white blood cells and from there travels to the brain. Once the parasite reaches the mouse’s brain, it overrides the animal’s innate fear of predators. By enhancing the neurotransmitter dopamine, toxo amplifies the mouse’s aggression and novelty-seeking behavior.

Toxo affect primal emotions like fear and anxiety, and even sexual arousal.[2]

In other words: Toxo hijacks the mouse’s brain and sends it straight into the claws and jaws of its predator.

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Toxo in humans

Toxo can also affect the behavior of humans. It has been shown to slow reaction times and decrease concentration.

This may explain why people involved in traffic accidents have been shown to be three times more likely to be infected with toxoplasmosis than others.

Through its influence on personality and risk-taking behavior, toxo may also be associated with some serious mental health conditions like schizophrenia, bipolar disorder, obsessive-compulsive disorder (OCD), and death by suicide.[3],[4]

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Toxo and entrepreneurship

Increased aggression and risk-taking behavior have their upsides: Toxo may play a surprisingly positive role in new business ventures.

The hormonal and neurological changes associated with toxo infection have the potential to enhance impulsive, reward-seeking, and risk-taking behaviors. Toxo infection may thus amplify one’s ambition, their pursuit of material possessions, and their connection to achievement.

Toxo may, in other words, enhance the characteristics associated with entrepreneurial activity.

A paper in the Royal Society Journal explores the association between infection and entrepreneurial activity. The paper reports that of 1,495 students surveyed, those who tested positive for T. gondii exposure were more likely to major in business. The researchers also found that toxo-positive professionals attending entrepreneurship events were more likely to have started their own business than the other attendees.[5]

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“But I don’t eat cat poop!”

Even though most of us don’t eat cat feces, we can still contract toxo by cleaning out kitty litter boxes. (Children can also get it by playing in sandboxes.)

We can also unknowingly ingest toxo oocytes from contaminated water, unwashed produce, or the under-cooked meat of animals prone to toxo infection (such as pigs). For this reason, it’s very important to drink clean, filtered water, to wash all produce, and to thoroughly cook meat products prior to consumption.

 

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Toxo risks in pregnancy

Toxo sometimes causes vague flu-like symptoms. More commonly, however, it has no observable symptoms and thus usually goes undiagnosed.

One noteworthy exception to this, however, is in the case of pregnancy.

A pregnant person should not empty the litter box.

Toxo may damage the brain or eyes of an unborn baby. It can also sometimes cause miscarriage or stillbirth. That’s why pregnant people are advised to avoid contact with kitty litter entirely.[6],[7]

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Why we still love cats

Despite the risks associated with toxo – or rather, perhaps because of those risks – we still love cats! Like the toxo-infected rats that find themselves attracted to felines, humans with toxoplasmosis may be more likely to enjoy cats and keep them as pets.

There’s also some thought that toxo infection may be linked to hoarding behavior (such as hoarding a bunch of cats!), though the theory is also still under investigation.[8] We may soon have a scientific explanation for the trope of the “Crazy Cat Lady.”

What is clear, however, is that whether you’re a budding entrepreneur, a road rager who gets into fender-benders, or just a person watching silly cat videos during your lunch break, you may very well have a protozoan parasite by the name of Toxoplasmosis gondii pulling your strings.

…And you are not alone: It’s estimated that over 2 billion people worldwide are infected with toxo.

Could that be why cats drive an estimated 15% of all Web traffic?[9] Is toxo the reason that cat videos have taken over YouTube?

The jury is still out, but the scientific evidence suggests: Quite possibly.

 

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References

[1] de Roode J. Is there a disease that makes us love cats? [Internet]. TEDEd [cited 2018 3 Dec]. Available from: https://ed.ted.com/lessons/is-there-a-disease-that-makes-us-love-cats-jaap-de-roode

[2] Zimmer C. EVOLUTION: Parasites make scaredy-rats foolhardy. Science. 2000 Jul 28;289(5479):525b-7b.

[3] Flegr J. How and why Toxoplasma makes us crazy. Trends Parasitol. 2013 Apr;29(4):156-63.

[4] de Barros JLVM, et al. Is there any association between Toxoplasma gondii infection and bipolar disorder? A systematic review and meta-analysis. J Affect Disord. 2017 Feb;209:59-65.

[5] Johnson SK, et al. Risky business: linking Toxoplasma gondii infection and entrepreneurship behaviors across individuals and countries. Proc Biol Soc. 2018 Jul 25;285(1883):20180822.

[6] Maldonado YA, Read JS. Diagnosis, treatment, and prevention of congenital toxoplasmosis in the United States. Pediatrics. 2017 Feb;139(2):e20163860.

[7] Hampton MM. Congenital toxoplasmosis: a review. Neonatal Netw. 2015;34(5):274-8.

[8] Royall DR. Toxoplamosis and hoarding [Internet]. Grantome; 2007 [cited 3 December 2018]. Available from: http://grantome.com/grant/NIH/M01-RR001346-26-6962

[9] Bennet L. “The Magazine Trying to Bring the Web’s Cat Obsession Offline” [Internet].  Bloomberg.com. February 19, 2015. Accessed September 6, 2022. Available from: https://www.bloomberg.com/news/articles/2015-02-19/catster-magazine-tries-to-bring-lolcat-world-into-print

Photo of cat and mouse by Dorothea OLDANI on Unsplash

Diagram of Toxoplasma gondii life cycle from: Transmission and Epidemiology of Zoonotic Protozoal Diseases of Companion Animals – Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Toxoplasma-gondii-life-cycle-Domesticated-and-wild-cats-are-the-definitive-hosts-of_fig2_234087025 [accessed 6 Sep, 2022]

Cat on laptop photo by Dorothea OLDANI on Unsplash

Feature photo by Bogdan Farca on Unsplash