There’s a parasite living in the gut of cats which sheds eggs which get eaten by rats, presumably from the cat droppings. The eggs hatch and form cysts in infected rats, including in their brains. However, how does the parasite complete its life-cycle and get back to the cat? It secretes a substance which causes infected rats to lose their fear of cats! Rats normally shy away from the smell of cat piss, however…

Rats carrying the parasite are for the most part indistinguishable from healthy ones. They can compete for mates just as well and have no trouble feeding themselves. The only difference, the researchers found, is that they are more likely to get themselves killed. The scent of a cat in the enclosure didn’t make them anxious, and they went about their business as if nothing was bothering them. They would explore around the odor at least as often as they did anywhere else in the enclosure. In some cases, they even took a special interest in the spot and came back to it over and over again.

But wait, there’s more. Humans can be infected with this parasite as well and it is associated with damage to a particular set of neurons. Schizophrenia is also associated with damage to those very same neurons, and anti-schizophrenia drugs also re-instate rats’ fear of cats, effectively curing them of the parasite’s effects! Is a cat parasite causing some cases of schizophrenia?

(full article)