 The brain parasite toxoplasma infects about one third of the populations of developed countries, about one in four adults in the US. But the lifelong presence of dormant stages of this parasite in the brain and the muscles of infected humans is usually considered asymptomatic from a clinical point of view. There's like this dynamic interplay between the parasite, the human brain, and our immune response that results in this détente that promotes the lifelong persistence of the parasite in our brain. We can't get rid of it, but at least we can keep it from killing us unless we get AIDS or something in our immune defenses drop. Within the past 10 years, however, many independent studies have shown that this parasitic disease could be indirectly responsible for hundreds of thousands of deaths due to its effect on the rate of traffic and workplace accidents, and also, suicides. Moreover, this latent toxoplasmosis is probably one of the most important risk factors for schizophrenia. Schizophrenia does have a strong genetic component, but even if you have the exact same genes as a schizophrenic, your identical twin has schizophrenia. The chances of you having it are still probably less than 50%. So what else might increase risk? Studies performed over five decades in 20 countries found toxoplasma infection nearly triples the odds of schizophrenia. That's more than any so-called schizophrenia gene that's been described so far. Now, obviously, everyone who gets this parasite in their brain does not come down with schizophrenia. It may depend on where exactly in the brain the parasite ends up taking up residence, but this increased prevalence of toxoplasma in schizophrenics has been demonstrated by at least 50 published studies. Yeah, but what about studies that weren't published? Maybe the ones that found no connection were just shelved or something. Even accounting for the so-called publication bias, the evidence of an association with toxoplasma seems overwhelming. Yeah, but it's still just an association. Instead of toxo, causing schizophrenia, maybe schizophrenia causes toxo. For example, institutionalized psychiatric patients may be fed undercooked meat, thereby increasing their exposure to toxoplasma infection. That's where the military studies come in. The U.S. military routinely collects and stores blood of its service members. This affords a unique opportunity to check people for infection, well, before the diagnosis of disease, so you can see which came first. And it was the toxo. The infection can be found prior to the onset of psychotic symptoms. The strongest evidence for a cause-and-effect role of toxoplasma in triggering schizophrenia comes from a recent MRI study, showing that differences in brain structure originally thought to be characteristic of schizophrenia patients were actually present only in those infected with the parasite. See, there's these gray matter anomalies, more often found in schizophrenia patients, but when you split them up into those testing positive and negative for toxo, you only really see it in the infected brains. So does that mean we might be able to treat schizophrenia with anti-parasitic drugs? Well, there is this tetracycline type drug that can kill off toxoplasma in mice, and when given to schizophrenics, does seem to improve symptoms. But the drug may also have independent anti-inflammatory and neuroprotective properties, so we don't know if it was a toxo-effect. Future research should look to delineate the anti-parasitic effect of minocycline by testing the patients for toxo to see if the drugs work better in those who have been infected. There have been four randomized controlled trials, specifically evaluating anti-parasitic drugs in patients with schizophrenia, and no effect was found. But incredibly not a single one of those studies used a drug that's been shown to actually kill off the parasites or once they've been walled off in the brain. See, after acute infection, the parasites form these cysts in the brain, leading to lifelong chronic infection, and drug resistance to commonly used anti-parasitics. There are currently no ongoing trials of anti-toxoplasma therapy in schizophrenia, despite ample evidence to justify further testing. I hope some researcher listening to this will realize that time is ripe to evaluate anti-parasitic drugs in toxo-infected patients with this horrible disease.