Normally a rat or mouse will keep to the shadows, thus avoiding cats. But when they are infected by toxoplasma the parasite completely changes their behavior. An infected mouse is attracted to the smell of cat urine and will move out into the open, displaying reckless behavior. The reason, of course, is the parasite wants the mouse to be eaten by a cat, so it can then infect its new host.
Humans also get infected by toxoplasma, though it is only really serious when a woman is pregnant as toxoplasma can damage the unborn child. But new research suggests that toxoplasma may influence us in more subtle ways.
We know, for example, that people who have antibodies to toxoplasma are more than twice as likely to be involved in a traffic accident. It could be that the parasite is making us, like rodents, behave in a more reckless fashion. Research also suggests it may slow down reaction times, with the intention of making us more vulnerable to large predators. Either way it is a chilling thought that parasites may be influencing how we behave in ways we do not yet begin to understand.
-How Parasites Manipulate Us, BBC News, 19 Feb 2014