Toxoplasma gondii, a parasite inhabiting the brains of an estimated three billion people, could tweak its host’s behavior
Scientific American MIND
Imagine a world without fear. It might be empowering to go about your daily life uninhibited by everyday distresses. You could cross highways with confidence, take on all kinds of daredevilry and watch horror flicks without flinching. Yet consider the prospect a little more deeply, and the possibilities become darker, even deadly. Our fears, after all, can protect us.
The basic aversion that a mouse has for a cat, for instance, keeps the rodent out of death's jaws. But unfortunately for mice everywhere, there is a second enemy with which to contend, one that may prevent them from experiencing that fear in the first place. A unicellular organism (a protozoan), Toxoplasma gondii, can override a rodent's most basic survival instincts. The result is a rodent that does not race away from a cat but is instead strangely attracted to it.