Brain Parasite Makes Mice Fearless

The Toxoplasma parasite is an unusually devious operator. When it infects mice, it alters their behaviour so they become fearless enough to seek out cats and get eaten. But exactly how it did this was a mystery.

Now it appears that the parasite hijacks its victim’s immune system, causing it to produce a chemical normally found in the brain. The discovery suggests that the brain and immune system might have evolved using similar processes to control their behaviour, including electrical and chemical signals now known mainly in nerves.