|"You have saved our lives. We are eternally grateful"|
Based on participants taking part in the Detroit Neighborhood Health Study exposure to T. gondii "defined by seropositivity and IgG antibody levels" was measured in approaching 500 people. Psychiatric diagnoses including depression, PTSD (posttraumatic stress disorder) and GAD were ascertained and data analysed to see if there was anything correlation-wise between T. gondii exposure and the various conditions.
The results suggested that T. gondii exposure was "associated with a 2 times greater odds of GAD" when taking into account various potential confounding variables. Those with some of the highest antibody levels to T. gondii were over three times at greater risk of GAD, potentially suggesting a dose-response relationship. Ergo, "T. gondii infection is strongly and significantly associated with GAD" but with more research to do.
Although no expert on GAD, I was a little puzzled by the Markovitz results. My previous musings on T. gondii and how it manages to alter rodent behaviour would seem to imply that this protozoan has an opposite effect on animal anxiety (i.e. reducing or modifying anxiety and predation-related fear ). Of course mice/rats are mice/rats and not humans but one might have expected something of an opposite effect .
That being said, this is not the first time that anxiety (human anxiety) has been mentioned alongside T. gondii as per the paper by Groër and colleagues  (open-access). In that case authors concluded that: "Higher T gondii immunoglobulin G titers in infected women were related to anxiety and depression during pregnancy". Some clarification is perhaps needed in this area...
To close, music I've probably linked to before but it's so good I'm gonna do it again: REM and It's the End of the World...
 Markovitz A. et al. Toxoplasma gondii and anxiety disorders in a community-based sample. Brain Behav Immun. 2014 Aug 11. pii: S0889-1591(14)00418-8.
 Kaushik M. et al. The role of parasites and pathogens in influencing generalised anxiety and predation-related fear in the mammalian central nervous system. Horm Behav. 2012 Aug;62(3):191-201.
 Gonzalez LE. et al. Toxoplasma gondii infection lower anxiety as measured in the plus-maze and social interaction tests in rats A behavioral analysis. Behav Brain Res. 2007 Feb 12;177(1):70-9.
 Groër MW. et al. Prenatal depression and anxiety in Toxoplasma gondii-positive women. Am J Obstet Gynecol. 2011 May;204(5):433.e1-7.
Markovitz A, Simanek AM, Yolken R, Galea S, Koenen KC, Chen S, & Aiello AE (2014). Toxoplasma gondii and anxiety disorders in a community-based sample. Brain, behavior, and immunity PMID: 25124709