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.

Nearly 500 participants with anxiety disorders (generalized anxiety disorder, post-traumatic stress disorder, and depression) participated in this study, and their blood was tested for a past Toxoplasma gondii infection. The researchers found that a past Toxoplasma gondii infection was linked to generalized anxiety disorder, but not post-traumatic stress disorder or depression. This was true even after the researchers adjusted for participants’ age, gender, race, income, marital status, and medication. In fact, those with a past history of infection were twice as likely as those without a past Toxoplasma gondii infection to have generalized anxiety disorder.

When the researchers took the severity of the Toxoplasma gondii infection into account (using the number of Toxoplasma gondii antibodies), they found a significant link between infection severity and generalized anxiety disorder. In fact, those with the most severe infections were three times more likely to have developed generalized anxiety disorder. In addition, Toxplasma gondii severity was not related to post-traumatic stress disorder or depression.

The authors concluded that these findings suggest that Toxoplasma gondii infection is “strongly and significantly associated with GAD [generalized anxiety disorder].” While this study cannot tell us whether Toxoplasma gondii can cause generalized anxiety disorder, the authors speculated that the parasite may play a role in the development of this disorder.

While the exact reasons for the association between Toxoplasma gondii and generalized anxiety disorder are still unclear, the authors point out that this will be an important direction for future research. Further research into the reasons for this association will help in treating and preventing this disorder.