Are Cat Parasites Controlling Your Brain?
Today's peer-reviewed study showing the enormous toll taken on wildlife by domestic cats is getting a lot of press, and rightly so. ("That Cuddly Kitty Is Deadlier Than You Think" in the New York Times is both the paper's "most viewed" and "most e-mailed" story of the day.) In the journal Nature Communications, authors Scott Loss,Tom Will, and Peter Marra find that
free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals.
The authors put the numbers at 1.4 to 3.7 billion birds killed annually in the United States, and 6.9 to 20.7 billion rodents. That's a lot of creatures. (Over at Mother Jones' Climate Desk, former Sierra intern Tim McDonnell helpfully put together a chart using the new numbers to put into perspective the much-lamented damage wind turbines do to birds, here.)
But here's the curious part. Why is this study getting so much more attention than the even more lurid indictment of felines in the current issue of Science News? "Little Mind Benders" by Susan Milius recounts how Toxoplasma gondii, a single-celled parasite that makes its home in the digestive tract of cats, "has wormed its way into an estimated one-third of people on the planet," lodging in their brains.
Studies comparing the infected and the noninfected raise the possibility that the parasite tweaks a person’s personality or ups the risk of suicide attempts, brain cancer and schizophrenia. Studies in people even report links between T. gondii and traffic accidents, greater odds of having sons than daughters, extra height and unusual opinions about the smell of urine.
T. gondii's effects on humans, it seems, are incidental to the world's creepiest reproductive strategy. The organism can only reproduce in the gut of a cat, and sends its offspring out into the world via the cat's feces, whence they hope to infect rats. Lodging in the rodents' brains, the organism causes them to "behave almost as if trying to become cat food."
A pounce and gulp from a cat is about the best thing that can happen to a parasite, but cat horror runs deep in rats. Even lab rats whose ancestors have not encountered cats for hundreds of generations normally avoid a catty scent.
When infected withT. gondii, however, rats became more active, a risk factor in itself for encountering a predator. They largely lost their reluctance to venture into test areas reeking of cat urine, and some of the infected rats actually spent more time in these urine-perfumed areas than in untainted refuges, Webster and colleagues reported in 2000. The parasite may possess an evolutionary trick that turns fear into a fatal attraction.
Take home advice from both stories: Keep kitty indoors, and be very careful when cleaning that litter box.
Photo of a cat with an American coot by Debi Shearwater, courtesy of the American Bird Conservancy.
PAUL RAUBER is a senior editor at Sierra. He is the author, with Carl Pope, of the happily outdated Strategic Ignorance: Why the Bush Administration Is Recklessly Destroying a Century of Environmental Progress. Otherwise he is a cyclist, cook, and father of two. Follow him on Twitter @paulrauber.