FACT OR FICTION: Toxoplasma gondii causes increased aggressive behavior in humans.

Present research is inconclusive and studies of the link are too fraught with confounding variables to be reliable, though some psychologists claim that Toxoplasma causes changes in human behavior, claiming that “men become less willing to submit to the moral standards of the community… [and] more distrustful of other people” while “women bcome more outgoing and warmhearted” (Zimmer 93). Attributing something as complex as human behavior to a parasite is difficult, though, and the complete and utter lack of controls means that the data is not compelling to most scientists. The link between Toxoplasma gondii and an increase in aggressive behavior in rats has been conclusively demonstrated (Berdoy 2000).

FACT OR FICTION: Toxoplasma gondii causes schizophrenia.

This is one of the most interesting controversies concerning T. gondii.

In a study using a rat model, scientists were able to demonstrate that the antipsychotic drugs used to treat schizophrenia are as effective at curbing aggressive behavior in the rats as antiparasitic medications. The antipsychotic drugs actually inhibited replication of T. gondii in cell culture (Webster 2003). This implies that the mechanism by which antipsychotic drugs work might include the inhibition of a parasitic infection. If this is the case, it has implications for the treatment of schizophrenia and suggests that the development of future drugs to treat the illness should focus on increasing the potency of the antiparasitic action.

E. Fuller Torrey and Robert H. Yolken are the two researchers most visibly tied to the theory that infection with T. gondii is implicated in schizophrenia. In their review of existing studies, they reported that out of nineteen existing studies on the subject, eighteen showed that schizophrenics had a higher concentration of T. gondii antibodies than non-sufferers with eleven of these studies showing a statistically significant difference. Of course, this correlation, even if it is true, does not prove causation. Still, the evidence is intriguing to many researchers.

But there could be another explanation for the seeming correlation between T. gondii and schizophrenia. Toxoplasmosis can result in the formation of cysts in the brain and acts on the central nervous system; increased rates of mental illness might just be a byproduct of this physical damage, not a Toxoplasma specific action.

Opposition to the link between T. gondii and schizophrenia comes from different camps. Some geneticists believe that the hypothesis neglects to give the effects of genes adequate credit for their role, though in the defense of proponents of the link, no research touts T. gondii as a sole causal factor of schizophrenia (Mihm). Other opponents see the research as part of a recent movement to ‘legitimize’ mental illness by locating a physiological root cause. Other people distrust researchers like Torrey, who is a fervent advocate of involuntary institutionalization of schizophrenics and ties his ‘obsession’ with the illness to his own sister’s experience with the disease. Many see him less as a scientist and more as an evangelist.

If Toxoplasma is conclusively linked to schizophrenia, the discovery would have far-reaching effects. First, it would allow researchers to learn more about the ways in which the disease operates on the brain (unlike some other neurological illnesses, schizophrenia does not appear in a highly patterned fashion, and as such is not as well understood as other illnesses). If schizophrenia is, as suggested by some scientists, the result of the interplay of genetics and parasitic infection, the isolation and treatment of at-risk populations might someday prevent the onset of schizophrenia.

But more important from a societal point of view, such a link would have the power to help destigmatize mental illness and to encourage that schizophrenia be treated with the same resources and sensitivity as other diseases. Research into mental illnesses is often under-funded as compared to so-called physical ailments; mental illness is seen more as a sign of weakness, and due to the ravages of disease (and oftentimes the socio-economic consequences of mental illness), schizophrenics are less equipped to advocate on their own behalf. But if researchers could frame their requests for funding as preventing a widespread parasite such as Toxoplasma gondii from putting the population at risk of schizophrenia, donors might be more willing to listen.

FACT OR FICTION: Toxoplasma gondii increases the likelihood that a woman will give birth to a male child.

In a study conducted at the Charles University in Prague, researchers found that women who tested positive for Toxoplasma gondii were significantly more likely to give birth to male children than women who were not infected. Using samples taken routing Toxoplasma scans over a ten-year period, researchers found that while the uninfected women gave birth to fifty-one boys for every one hundred live births, women infected with Toxoplasma gave birth to sixty boys per hundred. The women with the highest concentration of antibodies gave birth to seventy-two boys. The results were replicated in rats (Anitel 2006).

It is hypothesized that the parasite might act to inhibit spontaneous abortion, which usually affects more male fetuses because they are more often recognized by the mother’s body as a foreign body. But the body of research is at this time insufficient to prove a link, and no convincing hypotheses have emerged to explain why the parasite evolved in this manner. If this theory is proven, it could have significant effects because such a large portion of the population has Toxoplasma, and parents who have a sex preference for their children might believe that Toxoplasma infection significantly alters the chance of a favorable outcome. Also, such a significant effect might alter the widely held view that the parasite does not have many effects on human hosts except when they are immunocompromised.


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