Can cats who have been infected with the brain parasite, Toxoplasma gondii, really cause harm to people's mental health? Theoretically, researchers say, there have been studies that suggest the strong correlation between the two. But whether it actually happens, no evidence would be able to conclusively say.
Most of the evidence comes from rodents, which develop bizarre behaviors when infected with T. gondii. They lose their fear of the smell of cat urine, in some cases walking right into the jaws of waiting felines. Scientists think T. gondii alters brain function by forming cysts in regions that process fear and decision-making. The cysts may also affect behavior by ramping up levels of dopamine, a neurotransmitter involved in reward and risk-taking. There’s some evidence that T. gondii can rewire the brain permanently, making mice unafraid of cats even long after the parasite has been cleared.
Now, the problem with trying to test for the causal relationship between T. gondii and mental illnesses like schizophrenia is that it would be very difficult to test on humans. One can try to find people who have both been infected by T. gondii and have been diagnosed with schizophrenia or other mental disorders but it would be a challenge, to say the least, to determine whether they were infected first and then developed symptoms of mental illness or the other way around. Whatever the case may be, it would be best to stay cautious.
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