July 5, 2012
By Christie Wilcox
We human beings are very attached to our brains. We’re proud of them – of their size and their complexity. We think our brains set us apart, make us special. We scare our children with tales of monsters that eat them, and obsessively study how they work, even when these efforts are often fruitless. So, of course, we are downright offended that a simple, single-celled organism can manipulate our favorite organ, influencing the way we think and act.
Toxoplasma gondii is arguably the most interesting parasite on the planet. In the guts of cats, this single-celled protozoan lives and breeds, producing egg-like cells which pass with the cats bowel movements. These find their way into other animals that come in contact with cat crap. Once in this new host, the parasite changes and migrates, eventually settling as cysts in various tissues including the host’s brain, where the real fun begins. Toxoplasma can only continue its life cycle and end up a happy adult in a cat’s gut if it can find its way into a cat’s gut, and the fastest way to a cat’s gut, of course, is to be eaten by a cat. Incredibly, the parasite has evolved to help ensure that this occurs. For example, Toxoplasma infection alters rat behavior with surgical precision, making them lose their fear of (and even become sexually aroused by!) the smell of cats by hijacking neurochemical pathways in the rat’s brain.
Of course, rats aren’t the only animals that Toxoplasma ends up in. Around 1/3 of people on Earth carry these parasites in their heads. Since Toxoplasma has no trouble affecting rats, whose brains are similar in many ways to our own, scientists wonder how much the parasite affects the big, complex brains we love so much. For over a decade, researchers have investigated how this single-celled creature affects the way we think, finding that indeed, Toxoplasma alters our behavior and may even play a role in cultural differences beween nations.
The idea that this tiny protozoan parasite can influence our minds is old news. Some of the greatest science writers of our time have waxed poetic about how it sneaks its way into our brains and affects our personalities. Overall, though, the side effects of infection are thought to be minor and relatively harmless. Recently, however, evidence has been mounting that suggests the psychological consequences of infection are much darker than we once thought.
http://www.huffingtonpost.com/2012/07/0 ... &ir=Canada