A parasite that causes rats to sacrifice themselves to cats may also change human behavior, making women more outgoing and warmhearted, and men more jealous and suspicious. The Toxoplasma
bacteria protist is shed in cat feces, which are eaten by rats; infected rats become fearless in the presence of cats, which makes them easier to catch, which, in turn spreads the disease to new cats.
Carl Zimmer is the author of Parasite Rex, a sharp science book dealing with the amazing ways that parasites attack us, change us, farm us, use us and kill us. He reports on new research on the effect of Toxoplasma bacteria on humans.
Toxoplasma was previously believed to be largely harmless to humans (though it can compromise our immune systems). But new research suggests that humans, like rats, go through behavioral changes when infected with the parasite, though the effects are opposite in women and men.
Regular BB readers will remember my review of Scott Westerfeld's Peeps, a young-adult vampire novel largely inspired by Parasite Rex, in which all of the behaviors attributed to vampires are explained in parasitological terms.
Some scientists believe that Toxoplasma changes the personality of its human hosts, bringing different shifts to men and women. Parasitologist Jaroslav Flegr of Charles University in Prague administered psychological questionnaires to people infected with Toxoplasma and controls. Those infected, he found, show a small, but statistically significant, tendency to be more self-reproaching and insecure. Paradoxically, infected women, on average, tend to be more outgoing and warmhearted than controls, while infected men tend to be more jealous and suspicious.