Toxoplasma gondii and Behavior

Toxoplasmosis Appears to Cause Personality and Psychological Changes

Apr 17, 2007 Rosemary Drisdelle

Research on Toxoplasma gondii, a cat parasite, suggests that chronic infection causes subtle behavioral, personality, and psychological changes in infected people.

Toxoplasma gondii, a protozoan parasite, has people alarmed because of scientific evidence that it affects behavior—a disquieting ability that conjures up mental images of mind control and people run amok. Scientists are now zeroing in on the effects of toxoplasmosis on rats and mice; what the parasite does to cats and people, however, is still far from clear. Here are some results of research that help clarify what’s known at this time:

• Toxoplasma gondii parasites encyst in the tissues of warm-blooded hosts. (Read about Toxoplasma gondii in humans ). One of the places they tend to encyst is in the amygdala of the brain, the part that controls emotions—responses to social situations, sexual responses, aggression, fear, anxiety etc.
• During the 1980s and 1990s a number of scientists reported that T. gondii changed the behavior of mice and rats. Infected mice have increased activity levels and show increased aggression, and rats show a marked decrease in their natural fear of cat odors (Holliman, Lafferty)—changes that tend to make these rodents more likely to be eaten by a cat (Read about T. gondii in Cats).
• Rodents infected with T. gondii have increased dopamine levels, a neurotransmitter that is associated with novelty-seeking and neurotic behavior (Lafferty).
• Intriguing research on infected humans, published since the late 1990s, suggests that chronic infection causes subtle behavior changes in people too. Reaction time is affected, with possible implications for automobile accidents and other mishaps. Women seem to become more intelligent, outgoing, conscientious, sexually promiscuous, and kind; changes in men seem to cause opposite trends. All humans tend to be more prone to feelings of guilt (Flegr et al, Lindova et al).
• Studies show that people with schizophrenia and other mental health problems have a higher incidence of exposure to T. gondii than healthy controls, measured by the presence of antibody to the parasite (however, only about 15-20% of mentally ill people in these studies had antibodies).
• Antipsychotic drugs commonly used for people show activity against T. gondii parasites, and infected rodents show reduced behavioral changes when treated with these drugs (Webster et al).
• A recent study (Lafferty) explores the possibility that T. gondii may have effects at a cultural level in countries where many people are infected. The results support the hypothesis, but the author warns that there are significant weaknesses in the data, and that other factors significantly influence culture and social interaction, making T. gondii just one of many.

The effects of T. gondii on individual and collective human behavior are still not understood. Toxoplasma gondii may be doing damage, but it’s not on the scale of a mind-controlling monster in a science fiction movie. It’s important to remember that many factors influence human mental health and behavior—T. gondii is just one.

A short bibliography of peer reviewed journal articles on this topic:

Flegr J., Zitkova S., Kodym P. et al. “Induction of Changes in Human Behavior by the Parasite protozoan Toxoplasma gondii.” Parasitology. 1996 Jul; 113(Pt 1): 49-54.

Holliman R. E. “Toxoplasmosis, Behavior, and Personality.” Journal of Infection. 1997 35:105-110.

Lafferty, Kevin D. “Can the Common Brain Parasite, Toxoplasma gondii, Influence Human Culture?” Proceedings of the Royal Society B. doi:10.1098/rspb.2006.3641

Lindova J., Novotna M., Havlicek J. et al. “Gender Differences in Behavioral Changes Induced by Latent Toxoplasmosis.” International Journal for Parasitology. 2006 Dec; 36(14): 1485-92.

Webster J. P., Lamberton P. H., Donnelly C. A. et al. “Parasites as Causative Agents of Human Affective Disorders? The Impact of Anti-psychotic, Mood Stabilizer, and Anti-parasite Medication on Toxoplasma gondii’s Ability to Alter Host Behavior. Proceedings. Biological Sciences. 2006 Apr 22; 273(1589): 1023-30.

Read about another parasite that controls host behavior:

Horsehair Snakes

The copyright of the article Toxoplasma gondii and Behavior in Microbiology is owned by Rosemary Drisdelle. Permission to republish Toxoplasma gondii and Behavior in print or online must be granted by the author in writing.