I Ain't Scared of You

Toxoplasmosis.  If you are pregnant or are planning on becoming pregnant, this is one parasite you should know about and work hard at avoiding. It can pass through the placenta and negatively affect a growing fetus.  The consequences vary from mild to devastating.  It is transmitted to humans through cat feces.  It can be contracted from cleaning a cat litter tray, eating raw or undercooked meat, drinking unpasteurized milk, eating unwashed vegetables, working in the garden without gloves, or from exposure to a child's uncovered sandbox.

Dr. Rober Sapolsky calls it "Toxo."  He is a leading neuroscientist who is a professor of biology and neurology at Stanford University, as well as a research associate in Kenya.  He has received numerous awards for his scientific studies.  Here is an interview with him talking about Toxo.  It is fascinating and about 24 minutes long.  Well worth watching every minute, in my opinion.

In the life cycle of this parasite, it reproduces in the gut of a cat.  The eggs are shed in the feces, which are then picked up by rats and other animals that just might get eaten by a cat.  Toxoplasma forms cysts throughout the rat, including the brain. And yet a rat that is infected with it is perfectly healthy. That makes good sense for the parasite, since a cat would not be particularly interested in eating a dead rat. But scientists at Oxford discovered that the parasite "changes the rats in one subtle but vital way."

Rats respond negatively to the smell of a cat. The stress response in the rat goes up, and his instinct is to avoid the area where the smell was detected.  Makes sense.  When a rat is infected with Toxo, and smells a cat, the fear circuit in the rat does not activate.  Not only is he not afraid of the cat, but the sexual arousal circuit is activated slightly.  Wow!  This parasite has figured out how to get back into a cat so it can reproduce!  Just make the rat want to be around the cat, who will eat him.

When scientists in the UK looked at the genome (the genes and DNA) for Toxoplasma, they were astonished to find two versions of a gene that makes dopamine.  Dopamine is the neurotransmitter in the brain that is all about reward and anticipation of reward.  It is involved with emotional response, and the ability to experience pleasure and pain.  So in other words, this parasite has the gene that allows it to plug into the reward system of the brain.

So what about humans?  Can it affect our brains?  Besides the disaster of Toxo getting into the nervous system of a pregnant woman and her fetus, there are other things that go on in humans.

The first part of the infection might have symptoms like inflammation, sore throat, just not feeling well.  Then those symptoms disappear.  This is when the cysts form in the brain. For a rat, it is when the parasite makes the dopamine and the strange behavior of seeking out a cat occurs.  In men who are infected, their behavior can become impulsive.  Women less so.  There are two different groups, independent of each other, who have studied this and find that men who are affected are 3 to 4 times more likely to be killed in a high risk activity, such as reckless speeding in a car.

The personality of humans being changed by some invading organism is not a rare pattern.  The rabies virus changes both animal and human brains to become more aggressive. It knows how to make the host want to bite someone and pass on the particles of the virus.  And this parasite knows how to perpetuate its existence.

There are other areas that are being studied as having a possible link to Toxoplasma.  One is schizophrenia.  There is too much dopamine in the brain of a schizophrenic, and there is some evidence of a rate of increase to children whose mothers had cats when she was pregnant.  There are also questions about "cat women" being infected.  Scientist are still studying these and other aspects of this condition.

Now you have heard something interesting.