By Cristina Mancilla A new study finds that people infected with a protozoan could be more likely to engage in risky behaviors.
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A study by Johnson et al. found that people infected with Toxoplasma gondii are more likely to pursue entrepreneurship and participate in other risky behaviors . The protozoan T. gondii infects an estimated 2 billion people worldwide and has been shown to alter behavior in both humans and other warm-blooded animals. Johnson et al. tested thousands of US college students for T. gondii and compared the majors and interests between those who tested positive and negative . They also surveyed entrepreneur professionals. Students who tested positive for T. gondii were 1.4x more likely to major in business and 1.7x more likely to emphasize entrepreneurship. Among professionals, T. gondii infected individuals were 1.8x more likely to start their own business . Why would a protozoan encourage entrepreneurship? Animal behaviors often have an evolutionary explanation. Male peacocks have elaborate tail feathers because it’s more advantageous to reproduce than to be lightweight and run from predators. Dogs are loyal to humans because it was a survival mechanism in the past, but what benefit could a protozoan, a single-celled organism, possibly gain from encouraging their host to start a business? To answer these questions, let’s first look into the lifecycle of T. gondii. Although the protozoan can infect any warm-blooded animal, it can only reproduce in cat intestines. For centuries, T. gondii has been evolving to develop the best mechanism to be ingested by cats. Naturally, T. gondii chose to use mice. To increase transmission, the protozoan performs mind control T. gondii is able to reprogram a mouse’s brain from fearing cats to becoming sexually attracted to them. This “fatal attraction” phenomenon was first described in 2000  and has been heavily researched since. The protozoan manipulates mouse behavior through hypomethylation of certain regulatory elements which reprograms the brain to activate circuits responsible for sexual behavior upon exposure to cat odor . Even infected human males become sexually attracted to cat odor!
T. gondii also manipulates a mouse’s sense of fear and exploration  . Infected mice spend more time in open spaces and are generally less fearful. This behavior combined with an attraction to cat odor increases their chances of being eaten by a cat, just as T. gondii planned. So what does this have to do with entrepreneurship? The behavioral effects of T. gondii on humans are a consequence of their carefully crafted reproductive strategy of mice manipulation. Just like mice, scientists speculate that the protozoan could be manipulating humans in a similar, if subdued, way. The mechanism is not known, but studies have shown that T. gondii presence increases impulsivity in humans, particularly in young men and increases risk taking . Humans and mice share a striking amount of genetic and physiological similarities, which could explain the protozoan’s reach. Entrepreneurship is risky business and T. gondii may be interfering with the way people view danger and experience fear. Johnson et al. also found a positive correlation between countries’ entrepreneurship and business venture rates with the percentage of the population harboring T. gondii in their brains. Nations with higher infection rates also had a lower fraction of respondents experiencing “fear of failure” when pursing new business ventures. By infecting billions of hosts, the effects of T. gondii infection could amplify to drive grand, societal-scale patterns . Are we in control? These correlations highlight the relationships between infectious parasites and complex human behaviors. The results of the Johnson et al. study asks us to reconsider the role that microorganisms play in shaping our personalities, sexual attractions, and even career goals. T. gondii exemplifies the power that unseen/undetected creatures can have over one’s mind. We don’t need to visit haunted houses or shiver at the thought of invading Martians for Halloween thrills. Sometimes, nature can create its own little monsters – we only need to look within ourselves. __________________________________________________________________________________ References:  Johnson, Stefanie K., et al. "Risky business: linking Toxoplasma gondii infection and entrepreneurship behaviours across individuals and countries." Proceedings of the Royal Society B: Biological Sciences 285.1883 (2018): 20180822.  Berdoy, Manuel, Joanne P. Webster, and David W. Macdonald. "Fatal attraction in rats infected with Toxoplasma gondii." Proceedings of the Royal Society of London. Series B: Biological Sciences 267.1452 (2000): 1591-1594.  Flegr, J. and Markoš, A. “Masterpiece of epigenetic engineering – how Toxoplasma gondii reprogrammes host brains to change fear to sexual attraction”. Molecular Ecology, 23: 5934-5936 (2014): https://doi.org/10.1111/mec.13006  Tan, Donna, and Ajai Vyas. "Toxoplasma gondii infection and testosterone congruently increase tolerance of male rats for risk of reward forfeiture." Hormones and behavior 79 (2016): 37-44.  Boillat, Madlaina, et al. "Neuroinflammation-associated aspecific manipulation of mouse predator fear by Toxoplasma gondii." Cell reports 30.2 (2020): 320-334.  Cook, Thomas B., et al. "“Latent” infection with Toxoplasma gondii: association with trait aggression and impulsivity in healthy adults." Journal of psychiatric research 60 (2015): 87-94.