...And the Worms Ate Into His Brain

Are some viral memes created by viruses that cause memes?

A parasitic microbe commonly found in cats might have helped shape entire human cultures by manipulating the personalities of infected individuals, according to a new study.

Infection by a Toxoplasma gondii could make some individuals more prone to some forms of neuroticism and could lead to differences among cultures if enough people are infected, says Kevin Lafferty, a U.S. Geological Survey scientist at the University of California, Santa Barbara.

In a survey of different countries, Lafferty found that people living in those with higher rates of T. gondii infection scored higher on average for neuroticism, defined as an emotional or mental disorder characterized by high levels of anxiety, insecurity or depression...

T. gondii infects both wild and domestic cats, but it is carried by many warm-blooded mammals. One recent study showed that the parasite makes normally cautious rats outgoing and more prone to engage in reckless behavior, such as hanging around areas frequently marked by cat urine, making the rats easy targets.

Scientists estimate that the parasite has infected about 3 billion people, or about half of the human population. Studies by researchers in the Czech Republic have suggested T. gondii might have subtle but long-term effects on its human hosts. The parasite is thought to have different, and often opposite effects in men versus women, but both genders appear to develop a form of neuroticism called "guilt proneness."

Other studies have also found links between the parasite and schizophrenia. T. gondii infection is known to damage astrocytes, support cells in the brain that are also affected during schizophrenia. Pregnant women with high levels of antibodies to the parasite are also more likely to give birth to children who will develop the disorder.

In light of such studies, Lafferty wondered whether high rates of T. gondii infection in a culture could shift the average personality of its individuals.

"In populations where this parasite is very common, mass personality modification could result in cultural change," Lafferty said.

The distribution of T. gondii could explain differences in cultural aspects that relate to ego, money, material possessions, work and rules, Lafferty added. In some countries, infections by the cat parasite are very rare, while in others nearly all adults are infected...

Despite its association with neuroticism, Lafferty doesn't think all of the cat parasite's effects on human culture are bad.

"After all, they add to our cultural diversity," he said.

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