The effect of a parasite can sometimes go beyond the immediate health of the host. Sure, a tapeworm can steal nutrition, making the host weaker. Wasps sometimes lay their eggs inside other living insects, where they grow while eating their host. But some parasites go even further. Some of them can actually control the behavior of their host. It has to do with the life cycle of the parasite. If it’s presently in an ant and the next stage of its life cycle is in a grazing animal, for instance, the thing to do is make the ant climb to the top of a blade of grass where it can be conveniently eaten.
Half of all humans have in their brains a parasite of the type which is known to control the behavior of other animals. If they can control other animals, can they control humans?
We shouldn’t tar all parasites with the same brush. Some of them are fairly benign, even useful, as in the case of the pig whipworm. While the human whipworm infects half a billion people and can cause some problems, the pig whipworm doesn’t survive long in people. Just long enough to do its job, which is to treat inflammatory bowel disease, where the immune system gets overactive. Treatment involves drinking a concoction of pig whipworm eggs. It works by giving the immune system something to do, something it’s accustomed to doing like dealing with parasites, so it doesn’t attack the body’s own tissues. The results so far have been very encouraging. While drinking worm eggs might seem repulsive, it’s a lot better than an inflamed bowel.
Now back to the mind control parasites. There are hairworms that make grasshoppers jump into water so the worms can continue their life cycle there. There are flukes that make fish attract the attention of predatory wading birds. The flukes need to get into the birds. And there are the grass-climbing ants mentioned before.
The parasite which infects half of us humans is called Toxoplasma gondii. A version of T. gondii lives in rats and cats. Rats which have their brains infected are less likely to be scared off by the smell of cats and are more likely to be eaten. The parasite carries on in the gut of the cat.
Can this parasite affect the behavior of humans? There seems to be a link between it and schizophrenia. And drugs used to treat the disease halt the growth of the parasite in lab dishes. In the rats above, when they got the drug they became properly alarmed by the smell of cats again. It seems as if stopping the parasite also stops the strange behavior.
It’s time to break the strings of our parasitical puppeteers.