Toxoplasmosis (otherwise known as the cat poo parasite) has been linked to multiple psychological and behavioural differences in humans and new research suggests that infection can increase interest in entrepreneurialism and business.
But how seriously can we take studies like this? And what can toxoplasmosis actually do to humans?
Toxoplasmosis in the name of the infection caused by the parasite Toxoplasma gondii, which infects animals such as birds, cats, cattle, sheep, and goats as well as humans.
Toxoplasma gondii has been shown to aid its own transmission by changing the behaviour of its host.
The parasite affects rats by removing their innate fear of predators and making them more likely to be hunted – allowing Toxoplasma to infect and breed in the gut of their primary host, the cat.
This sort of parasite behaviour is not unprecedented in the animal kingdom, one parasitic worm causes grasshoppers to drown themselves by chemically influencing their brains.
In humans, toxoplasmosis has been linked to a number of neurological and behavioural differences including delayed reaction times (causing more traffic accidents), an increased attraction to the smell of cats, and schizophrenia.
A new study published by the Royal Society last week shows that people infected by toxoplasmosis are more likely to have entrepreneurial interests.
The study tested 1500 university students and found that those who tested positive for toxoplasmosis were more likely to major in business and to have an interest in management and entrepreneurship.
Among 200 professionals attending entrepreneur events, those who tested positive for the parasite were more likely to have started their own business compared with other attendees.
The authors of the study concluded that "infection prevalence [of toxoplasmosis] was a consistent, positive predictor of entrepreneurial activity".
However, it should be noted that the Royal Society study (and indeed all of the studies that show neurological or physical differences for infected people) is purely correlational, which means it only observed a statistical relationship and didn't use experimental controls.
So, can this parasite actually cause behavioural changes and schizophrenia in humans?
Associate Professor Chris Tonkin, a toxoplasmosis researcher from the Walter and Eliza Hall Institute of Medical Research in Victoria, told BuzzFeed News that we should be cautious with these research conclusions.
Tonkin notes that despite the correlational evidence, we still don't know what comes first: the parasite infection or the psychological and behavioural differences.
"Yes, it could be that toxoplasmosis somehow makes it more likely for these people to develop schizophrenia or to be more entrepreneurial but it could also be that the people that are more entrepreneurial or develop schizophrenia have more risk-taking behaviour and are therefore more likely to contract the parasite."
Despite toxoplasmosis' association with cat faeces, cleaning litter trays is not the only way it is possible to contract the parasite.
Handling or consuming undercooked meat, drinking contaminated water, or eating raw vegetables (cysts of Toxoplasma gondii eggs can live in the soil for years after exiting a cat) are all common modes of transmission.
Toxoplasmosis can also be transmitted in utero by infected mothers to their foetuses and this can cause extreme complications for foetal development including blindness, abnormal brain development such as microcephaly, convulsions, and foetal death.
However, it has been shown that these complications will only occur if the mother contracts toxoplasmosis for the first time during pregnancy – for mothers who already have the parasite before pregnancy, these foetal abnormalities will not be seen.
For healthy adults, toxoplasmosis is generally asymptomatic but it can cause flu-like symptoms such as headaches, muscle ache, and fever in people with compromised immune systems.
Currently, there is actually no evidence to say that Toxoplasma gondii inhabits human bodies in the same way that infects the bodies of other animals.
While the parasite is known to infect animals such as cows by lodging in cysts in muscle tissue and central nervous system (including the brain), there have been no studies to show that the parasite acts in the same way in the human body.
"Everyone assumes that they're [the cysts] are in the brain and the muscle but that's only in our studies from other animals," said Tonkin.
The greatest concern for human health that has come out of the toxoplasmosis literature is probably its correlational link to schizophrenia.
Multiple studies have shown that people who have schizophrenia are more likely to test positive for the Toxoplasma gondii antibodies that show a person has been infected by the parasite.
Two studies have also shown that exposure to cats in childhood is associated with developing the chronic mental illness.
However Tonkin emphasises that this link shouldn't be overblown.
"I'm personally not worried about it at all. I think that most people would be worried about mental illness and mental health...none of the studies say it's a definitive cause, that's a really important point. So when you get toxo [sic], it doesn't mean that you're going to get schizophrenia," he said.
While toxoplasmosis infection might be a risk factor in developing schizophrenia, Tonkin says it is just one of many other risk factors such as genetics or a traumatic upbringing.
Professor Joanne Webster, a parasite epidemiologist from Imperial College, London, also noted to Nature that the prevalence of toxoplasmosis varies from region to region, while schizophrenia has a blanket prevalence of 1% worldwide.
This suggests that toxoplasmosis would, at most, have a minimal effect on the risk of developing schizophrenia.
For Tonkin, there is still not enough evidence to conclusively show that Toxoplasma gondii has any effect on humans at all and the most interesting aspect of the parasite is still its effect on rat brains.
"No one understands yet how these pathogens do that because the brain and the central nervous system is such a remarkably complicated thing. How on earth does (what is a very simple organism generally) alter the complex organism?"