Q: Why Are Women Told Not To Clean Cat Litter Boxes During Pregnancy?

Many people assume this is an old wives tale, but this cautionary advice is actually based on true concerns. The reason is that cat litter and cat waste can contain a microscopic parasite named Toxoplasma Gondii, which can cause damage to the brain of a developing fetus.

Toxoplasma is a brain parasite whose primary hosts are rats, mice and cats, but the problem is that humans, too, can pick up and carry this parasite through exposure to cats. The Center for Disease Control and Prevention estimates that Toxoplasma gondii has infected about 22.5 percent of Americans older than 12-years-old. Once a person is infected it never goes away, but its inflammatory, active stage seems to be limited to several weeks after infection, then Toxoplasma appears to go dormant.

If you’re a mouse, picking up toxoplasma means bad news. “Toxoplasma manipulates the behavior of its animal host by increasing the concentration of dopamine and by changing levels of certain hormones,” notes Joroslav Flegr, a scientist who studies the parasite. (Rodriguez, 2012) In layman’s terms, the parasite makes a mouse’s brain circuitry go haywire, turning instinct on its head and making it so that they become fearless and are actually attracted to the scent of cats. This means the mouse gets eaten, and the parasite can spread and then complete its life cycle inside the gut of a new feline host.

Until very recently, Toxoplasma was believed to be entirely dormant and inactive in adult human hosts – something we carried but weren’t affected by. Yet recent research has cast major doubt on this belief. Studies have shown that on the whole, infected people tend to be more extroverted and less conscientious than infection-free participants. Those who are infected also have slightly higher rates of traffic accidents and higher rates of schizophrenia. (Rodriguez, 2012) So it appears that Toxoplasma may be capable of changing the brains of human hosts as well, just in far less profound ways.

In the brain of a developing baby, however, every small little change is amplified and these changes do become profound. Toxoplasma can lead to developmental delays and birth defects when a woman is newly infected during pregnancy. So stay away from cat litter boxes. We don’t want to be giving our babies brain parasites.