Take Two Tape Worms And Call Me In The Morning

Today I have a combination Medical Monday and Library Lizard post. I just read a very interesting book named Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures by Carl Zimmer. It tells you everything you ever wanted to know about parasites and more. I suppose everybody knows about some diseases that are transmitted by parasites, like malaria being caused by mosquitoes, or sleeping sickness being spread by flies. Most people have heard about the dangers of eating undercooked pork, which could be carrying Trichinella cysts.

One of the most interesting things I learned in this book is about the parasite named Toxoplasma gondii, that is spread by cats. Not many people know much about that parasite, even though a third of all the people in the world carry it around in their brains. In some places in Europe everybody has it. It usually moves back and forth between cats and rodents. A mouse gets infected by eating an egg, which hatches and produces little parasites in the mouse, which sit around waiting for the mouse to be eaten by a cat. Once in the cat they start the whole cycle all over again. People get infected by this parasite when they change contaminated litter pans. It's very important to make sure you aren't infected by this parasite if you are pregnant or want to get pregnant, because while the parasite doesn't severely affect adult human hosts, it will kill developing embryos.

The most interesting thing about this parasite is that it is one of many parasites that can change the behavior of it's host animal. It is able to make the little mouse more likely to be eaten by cats than uninfected mice. Researchers put rats in a controlled environment. They put different scents in each corner. One corner had the scent of fresh straw, one had the scent of other rats, another corner had rabbit scent, and the last one had cat scent. The healthy rats avoided the cat corner, but the infected ones either didn't mind the cat scent or actually preferred that corner.

The most interesting thing is how it affects humans who become infected. "Psychologists have found that Toxoplasma changes the personality of its human hosts, bringing different shifts to men and women. Men become less willing to submit to the moral standards of a community, less worried about being punished for breaking society's rules, more distrustful of other people. Women become more outgoing and warmhearted." So maybe the first thing they should do with male criminals is give them a good worming. It doesn't sound too bad for women, but I bet that's why there are so many little old ladies with 50 cats.

Another little piece of trivia from this book is a hypothesis about how the medical symbol of the stick with the snakes curled around it, the caduceus, got started. There is a parasite called guinea worms, that eventually leave your body by poking a hole in your leg and slowly crawling out. You have to let it crawl all the way out at its own speed or it will break in two and the half still in your leg will fester and you could die. The traditional way to remove a guinea worm is to just sit around and slowly wind the worm around a stick until the whole thing comes out. I assume after you get it all out you can stomp on it, or throw it in a fire, or whatever you want, but you have to be nice to it while it's still oozing out of your leg, which could take days because they can be two feet long and they're slow. I think I would rather get the Toxoplasma than the guinea worms.

Then there are diseases that seem to occur because you don't have any parasites. People in poor, developing countries don't suffer from asthma and allergies. Their immune system is too busy working with different parasites to worry about pollen or cat dander. Some scientists took a small group of people with ulcerative colitis and Crohn's disease, who didn't get any relief from standard medical treatment. They infected them with tapeworms and within a couple of weeks six out of seven had gone into complete remission.

Now you know.