Does Toxoplasmosis Cause Schizophrenia?

Michael Greger M.D. FACLM · May 27, 2019 · Volume 46

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A brain parasite is considered “probably one of the most important risk factors for schizophrenia.”

Discuss

Transcript

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The brain parasite toxoplasma “infects about one-third of the population” of developed countries—about one in four adults in the U.S. “But the life-long presence of dormant stages of this parasite in the brain and muscular tissue of infected humans is usually considered asymptomatic from the clinical point of view.” There’s like this “dynamic interplay between the parasite, [the human brain], and [our] immune response that results in this detente that promotes the life-long persistence of the parasite in [our brains].” We can’t get rid of it, but at least we can keep it from killing us—unless we get AIDS or something, and 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 effects 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 percent. 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 has 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 this so-called “publication bias,” “the evidence of an association with [toxoplasma seems] overwhelming.”

Yeah, but it’s still just an association. Instead of “toxo” (toxoplasma) 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 are 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 antiparasitic 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 antiparasitic effect of minocycline” by testing the patients for toxo to see if the drugs work better in those that have been infected. There have been “four…randomized controlled trials [specifically] evaluating antiparasitic drugs..in patients with schizophrenia,” and…no effect was found. But, incredibly, not a single one of those studies used a drug that has been shown to actively kill off the parasites, 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 antiparasitics.”

“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 “[t]he time is ripe to evaluate antiparasitic drugs in [toxo]-infected patients with [this horrible disease].”

Please consider volunteering to help out on the site.

Sources

Acknowledgements

Image credit: Tobias Berchtold via flickr. Image has been modified.

Motion graphics by Avocado Video

Topics

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The brain parasite toxoplasma “infects about one-third of the population” of developed countries—about one in four adults in the U.S. “But the life-long presence of dormant stages of this parasite in the brain and muscular tissue of infected humans is usually considered asymptomatic from the clinical point of view.” There’s like this “dynamic interplay between the parasite, [the human brain], and [our] immune response that results in this detente that promotes the life-long persistence of the parasite in [our brains].” We can’t get rid of it, but at least we can keep it from killing us—unless we get AIDS or something, and 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 effects 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 percent. 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 has 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 this so-called “publication bias,” “the evidence of an association with [toxoplasma seems] overwhelming.”

Yeah, but it’s still just an association. Instead of “toxo” (toxoplasma) 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 are 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 antiparasitic 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 antiparasitic effect of minocycline” by testing the patients for toxo to see if the drugs work better in those that have been infected. There have been “four…randomized controlled trials [specifically] evaluating antiparasitic drugs..in patients with schizophrenia,” and…no effect was found. But, incredibly, not a single one of those studies used a drug that has been shown to actively kill off the parasites, 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 antiparasitics.”

“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 “[t]he time is ripe to evaluate antiparasitic drugs in [toxo]-infected patients with [this horrible disease].”

Please consider volunteering to help out on the site.

Image credit: Tobias Berchtold via flickr. Image has been modified.

Motion graphics by Avocado Video

Doctor's Note

This is the third video in a four-part series on toxoplasmosis. If you missed the first two, start with Toxoplasmosis: A Manipulative Foodborne Brain Parasite and Long-Term Effects of Toxoplasmosis Brain Infection.

I dropped a few hints in this video (e.g. infections in muscle tissue), but stay tuned for the finale: How to Prevent Toxoplasmosis.

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