Cognitive Effects of Toxoplasma and CMV Infections: A Cross-Sectional Study of 557 Young Adults Considering Modulation by Sex and Rh Factor

One-third of humanity harbors a lifelong infection with Toxoplasma gondii . This parasite undergoes sexual reproduction in cats and asexual reproduction in any warm-blooded intermediate hosts. The cycle progresses as cats ingest these hosts, containing the parasite’s tissue cysts. Such infections can alter behaviors in both animals and humans, potentially increasing predation risk by felines—usually seen as parasite-induced manipulations. This study aims to delineate toxoplasmosis’s effects on cognitive abilities and compare these to the effects of human cytomegalovirus (CMV), which also infects the brain but is not spread through predation. We evaluated the cognitive performance of 557 students, who had been examined for Toxoplasma and CMV infections, using intelligence, memory, and psychomotor tests. Results indicated cognitive impairments in seropositive individuals for both pathogens, with variations in cognitive impact related to sex and Rh factor. Specifically, Toxoplasma was associated with lower IQ in men, whereas CMV predominantly with worse women’s memory and reaction speeds. Analysis of antibody concentrations hinted that certain Toxoplasma -associated cognitive detriments may wane (impaired intelligence) or worsen (impaired reaction times) over time following infection. The findings imply that cognitive impairments from both neurotropic pathogens are likely due to pathological changes in the brain rather than direct manipulative actions by the parasites.