Uncontrollable, explosive bouts of anger such a road rage might be the result of an earlier brain infection from the toxoplasmosis parasite, an organism found in cat feces, a new study finds. 
 
 In the study of more than 350 adults, those with a psychiatric disorder called Intermittent Explosive Disorder, or IED, were twice as likely to have been infected by the toxoplasmosis parasite compared with healthy individuals with no psychiatric diagnosis. 
 
 The study adds to a growing body of evidence suggesting that toxoplasmosis — usually a mild or nonsymptomatic infection from a protozoan parasite called Toxoplasma gondii — may somehow alter people's brain chemistry to cause long-term behavior problems. Previous studies have linked toxoplasmosis to schizophrenia, bipolar disorder, impulsivity and suicidal behavior. 
 
 The researchers stressed, however, that they merely have identified an association between toxoplasmosis and rage, and cannot say that toxoplasmosis causes rage — or that people should get rid of their cats, for that matter. 
 
 "Not everyone that tests positive for toxoplasmosis will have aggression issues," said Dr. Emil Coccaro, a professor and chairman of psychiatry and behavioral neuroscience at the University of Chicago, who led the study. But exposure to the parasite does appear to "raise the risk for aggressive behavior," and more research is needed to determine whether the link is causal, and what, if any, the underlying biological mechanism may be, he said.[The 10 Most Diabolical and Disgusting Parasites] 
 
 The study was published today (March 23) in the Journal of Clinical Psychiatry. 
 
 More than 20 percent of the U.S. population has been infected by the Toxoplasma parasite, according to the Centers for Disease Control and Prevention. Cats are the only known host in which this parasite reproduces; cats shed the parasites' eggs, called oocysts, in their feces. Humans can become infected after unintentionally ingesting the microscopic oocysts, primarily from not their washing hands after cleaning a cat's litter box or working in a garden with contaminated soil. Other sources of Toxoplasma are undercooked meat or unwashed vegetables that have been contaminated. 
 
 Toxoplasma can cause severe neurological problems and death in infants infected through their mothers during pregnancy, which is why pregnant women are advised not to change a cat's litter box. 
 
 Coccaro told Live Science he was intrigued by the body of scientific literature linking toxoplasmosis with psychiatric disorders. For this study, his research team recruited 358 adults. About one-third had IED, defined by the Diagnostic and Statistical Manual of Mental Disorders as recurrent, impulsive, problematic outbursts of verbal or physical aggression disproportionate to the situations that trigger them. Another one-third were individuals diagnosed with another psychiatric disorder (not IED). And the remaining third were healthy controls with no psychiatric history. 
 
 The research team found that 22 percent of the people with IED tested positive for toxoplasmosis exposure, compared with only 9 percent of the healthy control group. About 16 percent of the group with other psychiatric disorders tested positive for toxoplasmosis, too. 
 
 Jaroslav Flegr, a professor of biology at Charles University in Prague in the Czech Republic who was not involved in the study, said this was a confirmation of observations made by his research team over the last two decades. 
 
 "We have found that prevalence of toxoplasmosis correlates positively with violence-associated injuries and mortality in particular countries," said Flegr, who was among the first to propose that Toxoplasma can alter the brain. "It correlates also with diseases burden associated with bipolar disorder, obsessive compulsive disorder, and epilepsy. [10 Things You Didn't Know About the Brain] 
 
 All the researchers were at a loss, however, to explain how the infection could be tied to behavior. 
 
 "We don't yet understand the mechanisms involved," said Dr. Royce Lee, also of the University of Chicago, a co-author on the report. "It could be an increased inflammatory response, direct brain modulation by the parasite, or even reverse causation where aggressive individuals tend to have more cats or eat more undercooked meat." 
 
 Coccaro said that inflammation is a leading theory. Toxoplasmosis triggers the body to create antibodies, which are proteins that recognize specific pathogens and initiate the natural inflammation process to fight infections. After being ingested, Toxoplasma can travel to the muscles and the brain. In the brain, Toxoplasma can hide inside cells, and trigger an inflammatory response that damages nerve cells as the immune system attempts to kill the Toxoplasma. 
 
 One of the limits of the study, he said, was that his team could only assess the presence of antibodies in a blood sample, not a brain fluid sample. Future research may reveal the presence of Toxoplasma in the brain of those with IED, which could point in the direction of causation. 
 
 Or, conversely, doctors could treat IED patients for Toxoplasma infection to see if their symptoms reverse, Coccaro said. 
 
 Copyright 2016 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. ||||| They are cute, fluffy and have that wide-eyed glare that few of us can resist; it is no wonder more than 95 million of us own a cat. But there may be a darker side to our four-legged friends. New research claims the animals could increase our risk of mental illnesses, including schizophrenia and bipolar disorder. 
 
 
 
 Humans can become infected with Toxoplasma gondii by accidentally swallowing the parasite after coming into contact with a cat's feces. Humans can become infected with Toxoplasma gondii by accidentally swallowing the parasite after coming into contact with a cat's feces. 
 
 Two studies published in the journals Schizophrenia Research and Acta Psychiatrica Scandinavica attribute this association to Toxoplasma gondii - a parasite found in the intestines of cats. Humans can become infected with the parasite by accidentally swallowing it after coming into contact with the animal's feces. 
 
 T. gondii is the cause of a disease known as toxoplasmosis. According to the Centers for Disease Control and Prevention (CDC), more than 60 million people in the US are infected with the parasite, though the majority of people are not aware of it. 
 
 People with a healthy immune system often stave off T. gondii infection, so it does not present any symptoms. However, pregnant women and people with weakened immune systems are more susceptible to infection and may experience flu-like symptoms - such as muscle aches and pains and swollen lymph nodes - as a result, while more severe infection may cause blindness and even death. 
 
 Previous studies have also linked T. gondii infection to greater risk of mental disorders. In November 2014, for example, Medical News Today reported on a study claiming the parasite is responsible for around a fifth of schizophrenia cases. Now, new research provides further evidence of this association. 
 
 T. gondii infection 'may double schizophrenia risk' 
 
 For one study, Dr. Robert H. Yolken, of the Stanley Laboratory of Developmental Neurovirology at Johns Hopkins University School of Medicine in Baltimore, MD, and colleagues assessed the results of two previous studies. 
 
 These studies had identified a link between cat ownership in childhood and development of later-life schizophrenia and other mental disorders, comparing them with the results of a 1982 National Alliance for the Mentally Ill (NAMI) questionnaire. 
 
 The NAMI questionnaire - conducted around a decade before any data was published on cat ownership and mental illness - revealed that around 50% of individuals who had a cat as a family pet during childhood were diagnosed with schizophrenia or other mental illnesses later in life, compared with 42% who did not have a cat during childhood. 
 
 The questionnaire, the researchers say, produced similar results to those of the two previous studies, suggesting that "cat ownership in childhood is significantly more common in families in which the child later becomes seriously mentally ill." 
 
 "If true," the authors add, "an explanatory mechanism may be T. gondii. We urge our colleagues to try and replicate these findings to clarify whether childhood cat ownership is truly a risk factor for later schizophrenia." 
 
 In another study, A. L. Sutterland, of the Academic Medical Centre in Amsterdam, the Netherlands, and colleagues conducted a meta-analysis of more than 50 studies that established a link between T. gondii and increased risk of schizophrenia. 
 
 They found that people infected with T. gondii are at more than double the risk of developing schizophrenia than those not infected with the parasite. 
 
 The team also identified a link between T. gondii infection and greater risk of bipolar disorder, obsessive-compulsive disorder (OCD) and addiction. 
 
 "These findings suggest that T. gondii infection is associated with several psychiatric disorders and that in schizophrenia, reactivation of latent T. gondii infection may occur," note the authors. 
 
 The CDC recommend changing a cat's litter box every day to reduce the risk of T. gondii infection, noting that the parasite does not become infectious until 1-5 days after it has been shed in the animal's feces. 
 
 They also recommend feeding cats only canned or dried commercial foods or well-cooked meats; feeding them raw or undercooked meats can increase the presence of T. gondii in a cat's feces. 
 
 It is important to note that cat feces are not the only source of T. gondii infection. Humans can contract the parasite through consuming undercooked or contaminated meats and by drinking contaminated water. 
 
 In April, a Spotlight feature from MNT investigated toxoplasmosis and other health risks associated with pet ownership.
– People prone to angry outbursts are more than twice as likely to be infected with a common parasite called Toxoplasma gondii, which is often spread through cat feces. So report researchers in the Journal of Clinical Psychiatry, who looked for circulating antibodies to the parasite in 358 adults with intermittent explosive disorder (IED), non-IED psychiatric disorders (psychiatric controls), or no evidence of any psychiatric diagnosis (healthy controls). They found the parasite in just 9% of those without IED but 22% of those with it. Toxoplasmosis has been linked to schizophrenia, bipolar disorder, impulsiveness, and suicidal behavior, reports the Telegraph, but even so this finding surprised researchers. "We don't yet understand the mechanisms involved," coauthor Dr. Royce Lee of the University of Chicago tells Live Science. "It could be an increased inflammatory response, direct brain modulation by the parasite, or even reverse causation where aggressive individuals tend to have more cats or eat more undercooked meat." Indeed, the study establishes an association but not causation, and while the parasite can cause severe neurological problems and death in infants infected through pregnant mothers, it tends to cause far fewer problems in most of the 20% of Americans who've been infected by it. Researchers may next look for the parasite in the brains (instead of just bodies) of those with IED, or try treating IED patients for the infection to see if symptoms disappear. (Check out the broader range of issues the parasite is linked to in humans.)