Parasite Found in 1/3 of Human Brains Linked to Suicide, Schizophrenia

A tiny protozoan parasite called Toxoplasma gondii, once thought to be fairly harmless by scientists, is now being linked to both schizophrenia and suicide, the Huffington Post reported on Tuesday. 

Sometimes referred to as "the most interesting parasite on the planet," T.gondii can be found inside the heads of around 1/3 of all people. It is spread through contact with cat feces, and by eating undercooked meat or unwashed vegetables.

According to the HuffPo report, a 2006 study by E. Fuller Torrey of the Stanley Medical Research Institute in Bethesda, Maryland, were able to demonstrate the link between schizophrenia and the parasite by studying women with high levels of Toxoplasma - they found these women were more likely to give birth to future schizophrenics.

As for the link to suicide, the study worked like this: scientists in Denmark screened serum antibody levels of T.gondii in children from over 45,000 women in order to better understand how it's transmitted from mother to child. Because children don't form their own antibodies until they're three months old, the antibody levels were able to show how much of the parasite the mothers were carrying. The findings were clear and alarming. Women with T.gondii infections were 54% more likely to attempt suicide and twice as likely to succeed. Furthermore, women with the highest levels of the parasite were 91% more likely to commit suicide than those who were uninfected.

Unfortunately, scientists believe there's a good chance the parasite will soon affect an even higher percentage of people, thanks to climate change and the way we live in general.

But despite the evidence, scientists want to be clear: the link to suicide is a correlation, not causation.

"Is the suicide attempt a direct effect of the parasite on the function of the brain or an exaggerated immune response induced by the parasite affecting the brain? We do not know. We can't say with certainty that T. gondii caused the women to try to kill themselves," said Teodor T. Postolache, senior author of the study and an associate professor of psychiatry and director of the Mood and Anxiety Program at the University of Maryland School of Medicine.

"In fact, we have not excluded reverse causality as there might be risk factors for suicidal behaviors that also make people more susceptible to infection with T. gondii," he continued. "If we can identify a causal relationship, we may be able to predict those at increased risk for attempting suicide and find ways to intervene and offer treatment."