Do you consider yourself to be a ‘cat person’? Does your ideal future involve surrounding yourself with fluffy, contented feline friends? If you’ve ever owned a cat—or been in contact with undercooked meat, or unwashed vegetables—you may be carrying a parasite called Toxoplasma gondii.

If you do, you’re not alone—roughly one-third of the world’s population is thought to carry it. This parasite can cause an infection known as toxoplasmosis, which is generally thought to cause only mild flu-like effects in most people, though it can also cause serious inflammatory conditions of the eyes.

It is perhaps most famous for some of its claimed effects on human behaviour. Toxoplasmosis infections have been associated with an increase in aggressive and impulsive behaviours, a reduced perception of risk, and an increased probability of developing psychotic symptoms (such as schizophrenia). It is possible that the parasite’s effects on dopamine (a neurotransmitter, or brain chemical) and testosterone (a hormone) may be responsible. It’s also possible that people who already have certain personality traits or brain disorders are just more likely to become infected.

Read the full article at the Australian Academy of Science.