A study at the Walter Reed Army Institute of Research and Johns Hopkins Children's Center, has cited that being infected with the common Toxoplasma gondii parasite, carried by cats and farm animals, may increase the risk of schizophrenia.
The study led by Col. David W. Niebuhr, M.D. M.P.H. M.Sc., of Walter Reed Army Institute of Research, is believed to be the largest comparison of blood samples collected from healthy individuals and people with schizophrenia and was conducted among U.S. military personnel.
The findings revealed that out of the 180 study subjects diagnosed with schizophrenia, 7 pct were infected with toxoplasma much before their diagnosis as compared to 5 pct among the 532 healthy subjects. This implied that people exposed to toxoplasma had a 24 pct higher risk of developing schizophrenia.
Although the difference seems small, the researchers considered it to be important as the ability to explain even a small portion of the 2 million cases of schizophrenia in the United States may lead to clues to the disease and its possible treatments.
It was revealed that the majority of infections with toxoplasma occur early in life followed by exposure to the parasite in cat feces or undercooked beef or pork.
Although the infections rarely result in symptoms, the parasite remains in the body and can reactivate after lying dormant for years.
"Our findings reveal the strongest association we've seen yet between infection with this very common parasite and the subsequent development of schizophrenia," said Robert Yolken, M. D., a neurovirologist at Hopkins Children's who was among those conducting the analysis.
Yolken said that though previous studies have indicated link between schizophrenia and the presence of toxoplasma antibodies, which are evidence of past infection, but this is the first study to show that infection with the parasite can occur prior to the initial onset of symptoms and subsequent diagnosis with schizophrenia.
As the U.S. military regularly conducts tests on its active personnel for toxoplasma, among other infectious agents, and stores blood samples in a central repository, this made it possible for researchers to determine the time line between infection and a 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. With our current study, we were able to show that infection came first," said Yolken.
He also said that though most people infected with toxoplasma never develop schizophrenia, but the parasite can act as a trigger in those genetically inclined to the disorder this is a classic example of how genes and environment come together in the development of disease.
The study appeared in the recent issue of the American Journal of Psychiatry.