Research Suggests a Link between Toxoplasmosis and Mental Illness

The crazy cat lady – chicken or the egg?

Posted Jun 25, 2010

Women who are pregnant are warned against contact with cats in order to avoid acquiring the parasite Toxoplasma gondii. Recent research by Robert Yolken at Johns Hopkins Children's Center suggests that this is just the tip of the iceberg, and, as there is a growing body of evidence to suggest that toxoplasmosis may be linked to mental illnesses such as schizophrenia and bi-polar disorder in humans, the crazy cat lady may not have an overabundance of cats because she's crazy, but crazy because she has cats in the first place.

Toxoplasma gondii is a parasitic microorganism that has long been thought to be relatively benign in humans. Acquired by a pregnant woman, it has no demonstrable effect on her or her unborn child -- unless it crosses the placenta, where it can then have a devastating impact on the developing fetus.

Robert Yolken recently described his research into the link between toxoplasmosis and mental illness. He explained that Toxoplasma gondii experiences the world in one of two ways - cats and not-cats. The organism's preferred host is a cat, and it has the rather startling ability to actually alter the behavior of its non-cat hosts to increase the likelihood that it will interact with a cat, so it can then "jump" hosts.

For mice and rats, this means diminishing their natural "prey response" -- reducing their innate fear of cats -- increasing the likelihood that they will get eaten. For humans, Yolken and his colleagues found on the one hand a substantive increase in risk-taking behavior, which parallels the reduced prey response in rodents, but more interestingly, that the incidence of toxoplasmosis was almost double in schizophrenics.

The researchers reasoned that Toxoplasma gondii probably functions through the dopamine pathway and, as dopamine is known to be both abnormal in schizophrenia and play a role in depression, its presence exacerbates the tendency toward the development of these specific symptom profiles. It's not that toxoplasmosis itself causes schizophrenia or bi-polar disorder, but, rather, that its presence influences behavior through a disruption of the dopamine pathway, very much like the way that a disruption in the thyroid process can present as anxiety or agitated depression.

These findings led them to suggest two things; that there is a link between the presence of Toxoplasma gondii and the incidence of schizophrenia in humans, and that the presence of the parasite in non-affected individuals points to an increased potential for its later development.

The good news is that, just like eating a fat-rich diet only increases the potential for illnesses linked to high cholesterol or body fat, having Toxoplasma gondii in your system is not likely to drive you insane. However, if you feel that you may have been exposed to the parasite, a simple blood test - a request apparently being made more and more frequently -- can confirm or deny its presence.

And, more importantly for some, you don't have to get rid of your cat(s) - in fact, Yolken himself has three.


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