In his book Breaking the Spell Daniel Dennet briefly describes the fascinating Lancet fluke. It is a little parasite with an amazing life cycle (nicely described here). The little bugger reproduces in the liver of grazing mammals, but its eggs are excreted in their feces. That means that the larvae somehow need to get back into the grazing mammals. No problem, they can use mind control. Seriously.
The larvae get themselves eaten by ants and then, literally, take over the ants’ brains at night. Once into an ant, the larvae take control of part of the ant’s brain and cause it to climb to the top of a blade of grass every night. There they wait all night, hoping to get eaten (they only do this at night because during the day it would be too hot and the larvae would die).
If the ant hasn’t been eaten by morning it is allowed to return to normal behavior. Until the next night that is. Sooner or later a passing sheep/cow comes past at night and munches the grass and the little Lancet fluke is home free. Amazing.
The New York Times recently posted an article on similar parasite called Toxoplasma gondii which reproduces in cats. It needs a similar way of getting back into the cats after being excreted in feces and it does so by infecting the brains of rats. Rats infected by Toxo lose their fear of cats, and in fact are attracted to them. You can see where this is going…
The scary part of this story is that T. Gondii also infects people! Wired reports that it is estimated that more than 20% of people are infected. The exact impact on humans has not been conclusively proven yet, but it seems plausible that infected people would be attracted to cats.
You know that crazy cat lady next door? Maybe her brain has been infected by a mind altering parasite!