Microbes, Parasites, and Behaviour: Why the Human Body Does Not Speak with One Voice

A 2020 scientific review returned to a result studied for decades: a mouse infected with Toxoplasma gondii can show less avoidance of cat odour. This is not a horror-story detail. Toxoplasma is a one-celled parasite. It reproduces in cats and can pass through other animals. For a mouse, moving closer to a cat gives the parasite a better chance of returning to the host it needs to complete its life cycle. Animal experiments made one large idea hard to ignore: a very small organism can alter the behaviour of a larger host in a way that helps its own route of survival.