A study of 712 U.S. military personnel has found that those people who had been exposed to a parasite called toxoplasma gondii had a 24% higher risk of developing schizophrenia than their unaffected colleagues. Previous studies have shown a link between toxoplasma antibodies and schizophrenia but it has proved difficult to tell which of the diseases came first. Because the U.S. military routinely tests its active personnel for toxoplasma and stores the results in a central repository researchers were able to determine the time line between infection and a diagnosis of schizophrenia. Toxoplasma gondii is a common parasite carried by cats and farm animals and most infections with it occur early in life following an exposure to the parasite in cat faeces or undercooked beef or pork. Infections rarely cause symptoms but the parasite remains in the body and can reactivate after lying dormant for years. Not everyone who was infected with toxoplasma went on to develop schizophrenia suggesting that its effect can be affected by individual differences between its human hosts.
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