Schizophrenia can produce persistent delusions, hallucinations, and disorganized thinking. Its precise cause is unknown but seems to involve a combination of genetics and environmental risk factors. One of those environmental factors may be an infectious agent, such as the common parasite Toxoplasma gondii, which causes toxoplasmosis.
With cats being able to transmit Toxoplasma to humans, scientists have been investigating whether there is a link between cat ownership and schizophrenia. Many studies have tried to answer this question over the past 50 years; some studies show an association, but others do not. Researchers at the University of Queensland in Australia recently reanalyzed all these studies to determine the current consensus.
What Is Toxoplasma?
Toxoplasma is a single-celled parasite that infects all warm-blooded animals, including up to one-third of the human population. Cats are the only animals that support the sexual stage of the parasite’s life cycle, which culminates in the expulsion of infectious parasites in the feces. These fecal parasites are housed in sturdy containers called oocysts, which are stable in the environment for years and can spread the infection to a new individual if inhaled or ingested.
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In addition to litter boxes, people can pick up oocysts wherever a cat may have defecated, for example in the yard, sandbox, or garden (including unwashed fruits and vegetables). Oocysts have also made their way into streams and seawater, where they can infect people though shellfish.
Up to 40 million people in the U.S. are infected with Toxoplasma. While a healthy immune system can control the parasite’s growth, it cannot get rid of the infection entirely. Toxoplasma parasites remain in the brain and other tissues as latent cysts, which can resume growth if the immune system is weakened.
Most people with latent toxoplasmosis show no obvious signs of disease despite having parasite cysts in their brain. However, it has been noted that rodents with latent toxoplasmosis, which also show no signs of physical illness, do not behave normally. Most strikingly, infected rodents are more cavalier around threatening stimuli, including cat odors. Latent cysts have been shown to cause structural changes in the brain as well as alterations in hormones and neurochemistry.
Some studies suggest that the behavioral changes in mice may be caused by the immune response to the parasite, which causes inflammation in the brain.
Humans with latent toxoplasmosis appear to display similar neurological anomalies. Correlations between Toxoplasma infection and increased risk-taking, aggression and impulsivity, and suicide and homicide have been documented.
Regardless of the causes and effects of Toxoplasma infection, the studies remain inconclusive on its link with schizophrenia. Read on to learn more about the latest updates on this fascinating topic. » …
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