Parasite Rex


Parasite Rex was a complex book describing the life of a parasite. In todayís society, parasites are seen as useless creatures that live their lives at the expense of anotherís, but Carl Zimmer portrays them in a much different light. He brilliantly displays that parasites have received a poor reputation but are in fact a major contributor to life on earth today.

The beginning of the book describes how early scientists discovered parasites. Leeuwenhoek, Steenstrup and Koch, just to name a few, were the early scientists that discovered small creatures that seemed to infest others. One scientist, Ray Lankester, is responsible for parasiteís vicious reputation. He studied the parasite known as Sacculina, a parasite that inhabits crabs. He thought that it was born as a free-living organism that degenerated into a parasite, giving up the majority of its body to inhabit the body of another. Zimmer proved that these scientists were wrong about the evolution of the Sacculina, when in fact they are not degenerates, but rather very complex life forms.

The book continues on to describe the lives of several other parasites. One group is known as blood flukes, which inhabit the liver. One fluke, Schistosoma mansoni, lives in snails as their intermediate host where it waits to get into a human. Like all parasites, Schistosoma is specially adapted to survive the turmoil of the human body. It can navigate inside the abdominal cavity as if it had a road map. Along side the blood fluke is mentioned other parasites including Hookworms, Tapeworms and Trichinella. Parasitic wasps lay their eggs inside caterpillars where they feed upon the guts and intestines, sparing the vital organs. One particular parasite mentioned is Plasmodium, the parasite that causes malaria and is transmitted by hungry mosquitoes. Plasmodium has a very complex way of infecting the body and like all parasites can gracefully evade the immune system.

The next chapters of the book go into an in-depth description of the immune system. It tells exactly how the T and B cells are created and the complexity of their individual jobs. It describes bodies called Macrophages that engulf foreign bodies and chop them up to warn the body of potential danger. The bodyís immune system works well against viral and bacterial invaders but it is useless against parasites. They have their own cache of immune suppressing drugs that they pump into the body to fool it, change their coats or genetic make-up and some even use parts of their hostís body to disguise themselves. Some parasites, like Toxoplasma, actually stimulate the human immune system to keep itself in check, yet it does no harm to the human body. In many cases, it is not the parasite that kills itís host, for that would be at itís own disadvantage, but rather the hostís immune system that goes out of control, eventually harming the body instead of the invader. The equilibrium between the amount that parasite takes from the body and the harm that taking from the body actually causes is called ďvirulenceĒ.

Protozoa and single celled eukaryotes do not make up the entire parasite kingdom. In fact, fungi, insects, and some species of birds can actually do the same effect. Insects include parasitic wasps, which invade caterpillars, and parasitic flies, which invade leaf-cutter ants. Parasitic fungi can infect flies and cause them to die in a graceful position that is best for releasing the fungiís parasitic spores. Some bird species such as cuckoos lay their eggs in the nests of other birds and trick the other birds into caring for their eggs. In the book, many other parasites are mentioned along the way including nematodes, lancet flukes, guinea worms, Plasmodium (the parasite that causes malaria), Toxoplasma and various others.

Parasites tend to be numerous in closed areas such as areas of standing water, retention ponds and salt marshes. In salt marshes, the blood flukes in the water keep the population of fish and migratory birds under control. Without the parasites, the populations would run rampant and the delicate marsh ecosystem would be destroyed. There are no vaccines for parasites. A few crude attempts have been made, but to no avail. They have made certain drugs however, that can slow them down or even destroy them all