Toxoplasmosis Linked to Schizophrenia

Piece of the Puzzle

The largest comparison of blood samples ever collected turned up a link between infection from a parasite carried by cats and farm animals with an increased risk of schizophrenia. Scientists discovered that out of the 180 study participants diagnosed with schizophrenia, 7% of them had been infected with the common Toxoplasma gondii parasite prior to diagnosis, as compared to 5% among the remaining 532 participants in good mental health. This means that individuals exposed to toxoplasma show a 24% increase in the risk of developing schizophrenia. Though the difference may seem small, it is a significant piece of the puzzle in helping us to understand this disease and its possible treatments.

Halt the Progression

One result of these findings is the planning of a further study to determine whether aggressive treatment of the toxoplasma infection with antiparasitic drugs in those patients with schizophrenia might halt the progression of this mental disorder, which is characterized by delusions, hallucinations, and paranoia.

Infection from toxoplasma tends to occur early in life after exposure to the parasite by handling soil contaminated by cat feces or by ingesting undercooked beef or pork. The infection doesn't often cause symptoms, but the parasite may remain dormant in the body and can reactivate after many years have passed.

The findings of this study were published in the January issue of the American Journal of Psychiatry. The participants of the study were culled from U.S. military personnel by researchers from the Walter Reed Army Institute of Research and Johns Hopkins Children’s Center. Among those who worked to analyze the information was Robert Yolken, M. D., a neurovirologist at Hopkins Children’s who commented that these findings showed the strongest association yet seen between an infection by a parasite and the subsequent development of schizophrenia.

Past studies had shown a link between schizophrenia and the presence of toxoplasma antibodies as evidence of earlier infection, but this was the first study to show that the parasite precedes the onset of symptoms or a diagnosis of the ailment. The U.S. military counts toxoplasma among routine tests carried out on personnel. Blood samples are then stored in a central repository, so that researchers found it possible to determine a time line between the contraction of the infection and a subsequent diagnosis of schizophrenia.

 “Until now, the only thing we could say is that some people with schizophrenia also had been infected with toxoplasma at some point, but we couldn’t tease out which came first,” said Yolken. “With our current study, we were able to show that infection came first.”

Most people infected with toxoplasma never go on to develop schizophrenia; however, those who are susceptible to the disorder may find that the contraction of the parasite triggers the disorder. This would be an example of how genes and environmental factors work in tandem toward the development of a mental illness, said Yolken.

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