Toxoplasma gondii is one of the most common parasites in humans, affecting as much as one-third of the world’s population. Individuals can become infected with this parasite in several ways, such as by eating undercooked meat, drinking unpasteurized milk, or eating raw fruits and vegetables. In addition, the Toxoplasma gondii’s eggs are present in cat feces, and one of the most common way people are infected with Toxoplasma gondii is through contact with an infected cat.

In individuals with a weakened immune system (such as infants or those with HIV/AIDS), the Toxoplasma gondii parasite can cause serious, and even fatal, illness. Because of this, experts recommend that pregnant women do not clean a cat’s litter box.

A study published in the journal Brain, Behavior, and Immunity investigated whether a past history of Toxoplasma gondii infection was related to anxiety disorders, which affect about 6% of individuals sometime during their lifetime. The Toxoplasma gondii parasite has been linked to several mental disorders, but no past research has examined whether this parasite is implicated in anxiety disorders.