According to the Mayo Clinic and the CDC, contact with the Toxoplasma parasite can cause a flu-like illness called Toxoplasmosis. Symptoms include aches and pain, swollen lymph nodes, fever, fatigue, and in severe cases, eye inflammation, poor coordination, confusion, and seizures. Cat litter, contaminated or unwashed foods and utensils, and infected blood can transmit the parasite. However, most of the 60 million Americans who carry the parasite are symptom-free because their immune systems are strong enough to deter infection.

But some individuals have a more sinister view of the parasite. In an article for The Alantic by Kathleen McAuliffe, Czech scientist Jaroslav Flegr stated that the parasite could be subtly affecting infected individuals’ psychologies. Flegr believes that the parasite causes greater social anxiety, which explains why his research found that infected women were more outgoing and image-conscious, while infected men were more suspicious and introverted. Infected people also had delayed reaction times, which Flegr suspected was a cause for car accidents. Moreover, a study at Charles University found that decreased brain volume in schizophrenia was associated with patients who tested positive for the parasite, suggesting that the parasite can cause this psychological disease in genetically susceptible people. Flegr suggested that the parasite can cause people to be drawn to cats too!

Toxoplasma gondii reproduces in cats. However, it also infects mice, which transmit the disease to other cats when eaten. The parasite alters chemicals in rodents’ brains, taking away their fear of cats. In fact, the parasite rewires the pleasure centers of a mouse’s brain, causing mice to be drawn to cat odor and therefore eaten. With these findings, Flegr’s theories seems more plausible. In fact, other microbes behave in a similar way; McAuliffe’s article compared T. gondii to the rabies virus, which also alters psychology, often causing animals to become anxious and vicious. By causing neurological stress in a rabid animal, the virus makes the animal more likely to bite and thus transmit the infection to other animals.

Unlike the rabies virus, though, T. gondii does not kill the majority of infected people. According to Carl Zimmer in The New York Times, the parasite is the Trojan horse of the microbe world, stealthily infecting mammals and evading the notice of their immune systems. By letting its host live, the parasite has a greater opportunity to find a new host feline to infect. However, the parasite can cause severe symptoms in infants, explaining why pregnant women are advised to avoid contact with cat litter. Patients with compromised immune systems must be especially cautious too. Zimmer’s article concludes that risk of infection is one reason to keep cats indoors. T. gondii is also a reason to consider cooking meats thoroughly and washing store-bought or hand-picked produce before eating it.

Mind-controlling parasites? Sounds like science fiction! Luckily, we can live with T. gondii. It’s no reason not to love cats or cat-lovers, but it encourages us to be more careful and aware of our surroundings.