Common Infection Linked To Schizophrenia

Candida albicans is a common yeast normally found in small quantities in the gut. Mukhina Viktoriia/Shutterstock

People suffering from mental illnesses like schizophrenia and bipolar disorder may have their gut microbes to blame, after a new study found that those with these conditions are more likely to have been infected with a type of yeast called Candida albicans at some point in their lives. Interestingly, this association was only observed in men, although the researchers found that schizophrenic and bipolar women who had experienced similar infections tended to perform worse on memory tests than those who had not been infected.

Small populations of C. albicans are found in the gut of most people, and are kept in check by the body’s immune system, which prevents the yeast from overgrowing. However, when the immune system fails, the fungus can rapidly proliferate, causing some nasty side effects like thrush.

As previous studies have shown, some bacterial and fungal infections can damage the development of the brain and central nervous system as these microbes release certain toxic chemicals into the bloodstream – some of which may be able to cross the blood-brain barrier. While these toxins may be dealt with appropriately by a healthy immune system, people with immune deficiencies may not be protected against their damaging effects.

For instance, it was recently found that people who suffer from uncontrollable bouts of rage are more likely to have been infected by a single-celled parasite known as Toxoplasma gondii – often transmitted by their pet cat – while some acids released by certain species of yeast have also been implicated in autism.

As such, it may not be the microbes themselves that are responsible for the development of these mental disorders. Rather, the inability of the body’s immune system to remove certain substances could be the root of the problem. Accordingly, study co-author Emily Severance explained that "it's far too early to single out Candida infection as a cause of mental illness or vice versa."

The paper, which appears in the journal npj Schizophrenia, outlines how researchers examined levels of an antibody called immunoglobulin G (IgG) in the blood of several hundred patients with schizophrenia and bipolar disorder. IgG class antibodies are recruited by the immune system to fend off Candida infestations, so high concentrations of these antibodies in the blood are a good indicator of a past infection.

The causes of schizophrenia are still not fully understood. Oleg Golovnev/Shutterstock

Results showed that, compared to people who do not suffer from these psychiatric conditions, men with schizophrenia and bipolar disorder were 12 percent more likely to have experienced overgrown C. albicans. Intriguingly, however, infection rates were no higher in schizophrenic and bipolar women than in healthy women.

Yet when asked to conduct a number of tests designed to measure memory, attention, and visual-spatial skills, schizophrenic and bipolar women who had high IgG class antibody levels performed significantly worse than those with similar mental illnesses but low antibody levels.

Therefore, while the study authors conclude that it “may be premature to list this pathogen as a risk factor for disease causation,” they do insist that the correlation between infection rates and cognitive impairment is worthy of attention. As such, Severance advises that “clinicians should make it a point to look out for these infections in their patients with mental illness.”

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