The study, published in the the American Journal of Psychiatry, found of the 180 study subjects diagnosed with schizophrenia, 7 percent had been infected with toxoplasma prior to diagnosis, compared to 5 percent among the 532 healthy military recruits.

The 24 percent higher risk of developing schizophrenia among those infected with taxoplasmas may seem small but it is important because explaining even a small portion of the 2 million cases of U.S. schizophrenia could offer clues to the disease, the researchers said. The researchers said they will study whether aggressive treatment with anti-parasitic drugs affects progression of schizophrenia.

"Our findings reveal the strongest association we've seen yet between infection with this very common parasite and the subsequent development of schizophrenia," study investigator Dr. Robert Yolken of John Hopkins Children's Center in Baltimore said in a statement.

Most infections with toxoplasma gondii parasite occur early in life following exposure to the parasite in cat feces or undercooked beef or pork. Infections rarely cause symptoms but the parasite can be dormant for years.