We've known for several years that strep infections in children can cause OCD.
A likely mechanism by which a bacterial infection triggers obsessive compulsive disorder (OCD) in some children has been demonstrated by scientists at the National Institutes of Health's (NIH) National Institute of Mental Health (NIMH) and collaborators at California State University (CSU) and the University of Oklahoma (UO). Their research suggests that an antibody against strep throat bacteria sometimes mistakenly acts on a brain enzyme, disrupting communications between neurons and causing a form of obsessive compulsive and related tic disorder in children — pediatric autoimmune neuropsychiatric disorders associated with streptococci (PANDAS).And we've known that toxoplasmosis, a parasitical infection caused by Toxoplasma gondii, can cause behavioral changes in animals and in humans.
...T. gondii-infected rodents exhibit an increase in activity and a decrease in predator vigilance behavioural traits (Berdoy et al., 1995; Hay et al., 1983; Hay et al., 1984; Hutchison et al., 1980a; Hutchison et al., 1980b; Lamberton et al., 2008; Webster, 1994; Webster, 2001; Webster, 2007; Webster et al., 1994; Webster et al., 2006). Moreover, whilst uninfected rats show a strong innate aversion to predator odour, T. gondii infection appears to subtly alter the rats’ cognitive perception of cat predation risk, turning their innate aversion into a ‘suicidal’ ‘fatal feline attraction’ (Berdoy et al., 2000; Vyas et al., 2007c; Webster et al., 2006). Such fatal feline attraction appears specific towards a response to cat (urine) odour, with no difference observed between infected and uninfected rats in their responses to odours of non-predatory mammals such as rabbit (Berdoy et al., 2000; Vyas et al., 2007c; Webster et al., 2006) nor contrasting potential predatory species odours such as mink (Lamberton et al., 2008) or dog (Kannan et al., 2010).
Consistent with a possible impairment in psychomotor performance and/or enhanced risk-taking personality profiles, individuals with latent toxoplasmosis have been reported to be at a 2.65 times increased risk to be involved in a traffic accident relative to the general population (Flegr et al., 2002), a result subsequently replicated by other groups (Flegr et al., 2009; Kocazeybeka et al., 2009; Yereli et al., 2006). Another recent study, albeit significant only in a subset with lower socioeconomic status, linked T. gondii seropositivity with workplace accidents (Alvarado-Esquivel et al., 2012). There is also the ever growing and convincing body of evidence concerning a potential relationship linking T. gondii with that of some forms of affective and neurological disorders in humans. Correlations have been found for OCD (Miman et al., 2010b), Parkinson’s disease (Miman et al., 2010a), Alzheimer’s disease (Kusbeci et al., 2011), suicide (Arling et al., 2009) and bipolar disorder (Pearce et al., 2012). The most substantial body of empirical evidence gathered to date relates to the potential association between T. gondii and some cases of schizophrenia in humans. T. gondii seroprevalence has been associated with schizophrenia in at least 38 studies to date (Mortensen et al., 2007; Torrey et al., 2007; Torrey et al., 2012; Torrey et al., 2000; Torrey and Yolken, 2003; Yolken and Torrey, 2008).There's even been speculation about T. gondii causing cultural differences.
The associations between prevalence and cultural dimensions are consistent with the prediction that T. gondii can influence human culture. Just as individuals infected with T. gondii score themselves higher in the neurotic factor guilt-proneness, nations with high T. gondii prevalence had a higher aggregate neuroticism score. In addition, Western nations with high T. gondii prevalence were higher in the ‘neurotic’ cultural dimensions of masculine sex roles and uncertainty avoidance. These results were predicted by a logical scaling-up from individuals to aggregate personalities to cultural dimensions.So when we read about people traveling to the Middle East, or associating with folks from the ME in their mosques and whatnot, and their being suddenly and inexplicably "radicalized" ... see where I am going with this?