The Cat Parasite

Toxoplasma gondii can reproduce sexually only inside cats. To get there, it often passes through rodents. In classic studies, infected rodents showed reduced aversion to cat odor, making them easier prey.

That is a striking host-manipulation story, but not a perfect one-behavior edit. Later work suggests broader changes in activity, risk, and brain signaling may also be involved.

Inside the rodent, Toxoplasma forms cysts, including in brain tissue. Studies link infection to changes in fear circuits, dopamine-related signaling, and risk behavior.

The mechanism is still being worked out. The important point is that a parasite can alter host behavior in ways that may improve its own chances of reaching the next host.