A parasite common in cats
can eliminate infected mice’s fear of felines — a brain hijack that leads to a
potentially fatal attraction. But this cat-related boldness (SN: 9/18/13) isn’t the
whole story.

Once in the brain, the single-celled
parasite Toxoplasma gondii makes mice reckless in all sorts of dangerous scenarios, researchers
write January 14 in Cell Reports. Infected
mice spent more time in areas that were out in the open, exposed places that
uninfected mice usually avoid.

Infected mice also prodded
an experimenter’s hand inside a cage — an intrusion that drove uninfected mice to the other
side of the cage. T. gondii–infected mice were even unfazed by an anesthetized
rat, a mouse predator, the researchers from the University of Geneva and
colleagues found. And infected mice spent more time than uninfected mice
exploring the scents of foxes and relatively harmless guinea pigs.

The extent of mice’s infections,
measured by the load of parasite cysts in the brain, seemed to track with the
behavior changes, the researchers report.  

Toxoplasma gondii
Toxoplasma gondii, tweaked to glow green, was isolated from the brain of an infected mouse.Pierre-Mehdi Hammoudi, Damien Jacot

The parasite needs to get
into the guts of cats to sexually reproduce. Other animals can become infected
by ingesting T. gondii through direct
or indirect contact with cat feces. The parasite can then spread throughout the
body and ultimately form cysts in the brain.

People can become infected
with T. gondii, though usually not as
severely as mice. Some studies have hinted, however, at links between the
parasite and human behaviors such as inattention and suicide, as well as mental
disorders such as schizophrenia.