Common Parasite Linked to Personality Changes

It appears that about 22 percent of the American public, over the age of twelve, is infected with a parasite that can influence behavior. People infected with the microscopic parasite Toxoplasma gondii are more extroverted and less conscientious than those that are not infected and that the longer men are infected the less conscientious they become.

Here's a link to the Scientific American article this came from.