How a cat parasite can change your personality

A new study suggests that infection with the cat-borne parasite Toxoplasma gondii could make people more risk-prone and likely to start their own business.

As humans who still inherit Enlightenment's worship of rationality, we like to think that our decisions are autonomous and driven by reason alone.

However, science seems to contradict this popular belief. More and more research is showing that microorganisms such as bacteria and viruses influence our behavior and emotional states.

For instance, the bacteria in our guts may be responsible for states of anxiety and depression. Conversely, other studies have shown that some probiotic bacteria may relieve the effects of stress.

Now, a new study suggests that infection with the cat-borne parasite Toxoplasma gondii could make people change their behavior so that they become more prone to business and entrepreneurial ventures.

Stefanie K. Johnson, an associate professor at the University of Colorado (CU) Boulder's Leeds School of Business, co-led the research in collaboration with Pieter Johnson, a professor in CU Boulder's Department of Ecology and Evolutionary Biology.

The findings were published in the journal Proceedings of the Royal Society B.

What is T. gondii?

T. gondii is a protozoan parasite — that is, a single-celled microorganism that can reproduce itself — that usually infects wild and domestic cats.

According to the Centers for Disease Control and Prevention (CDC), the parasite infects 11 percent of the population of the United States over the age of 6.

Previous studies have correlated T. gondii infections with impulsive and risky behavior, as well as with a higher risk of car accidents, mental health issues, substance abuse disorders, and suicide.

Some have speculated on the evolutionary explanation for this parasite's effects. Because the parasite reproduces in cats' guts, the hosts' behavior needs to change in a way that makes it more likely for them to be eaten by a feline.

Studies in rodents support this hypothesis, showing that mice that are infected with T. gondii lose their fear of cats.

Studying T. gondii in humans

Johnson and colleagues took saliva samples from almost 1,500 undergraduate students and found that people who tested positive were more likely to be interested in business and management.

Specifically, T. gondii-positive people were "1.4 [times] more likely to major in business and 1.7 [times] more likely to have an emphasis in 'management and entrepreneurship' over other business-related emphases."

The team also carried out another survey of almost 200 adults who took part in entrepreneurship events. This revealed that people with T. gondii were 1.8 times "more likely to have started their own business compared with other attendees."

Finally, Johnson and team also examined national statistics of T. gondii infections from over 42 countries and found that infection with the parasite consistently predicted entrepreneurial activity.

They also found that countries with the highest rate of infection had the lowest numbers of people who were likely to mention a "fear of failure" as the main reason they wouldn't start a business venture.

Parasite may reduce rational fear of failure

Stefanie K. Johnson reflects on the meaning of these findings, saying, "We can see the association in terms of the number of businesses and the intent of participants, but we don't know if the businesses started by T. gondii-positive individuals are more likely to succeed or fail in the long run."

"New ventures have high failure rates, so a fear of failure is quite rational. T. gondii might just reduce that rational fear."

Stefanie K. Johnson

Pieter Johnson also chimes in, saying, "Infectious diseases have strongly shaped human history and culture over millions of years."

"Today, we like to believe our decisions and destiny are ours alone, but the contributing roles of our microscopic companions are increasingly apparent."