Iremember reading about the use of leeches in old timey medicine - like from the Middle ages. As old fashioned and seemingly ridiculous as it sounds, it seems like the doctors of that time might have been on to something. I just read in BusinessWeek that scientists have discovered that the eggs of parasites can help treat a range of vexing diseases.
An example are microscopic size whipworm or hookworm eggs which apparantly can be used to treat almost 60 different autoimmune diseases such as Crohn's disease and Multiple Sclerosis. Maggots can be used to clean wounds.
Why are we finding that these parasites work? It seems that as a civilization we have become "too clean" so that our bodies are not able to fight certain infections and diseases the way they used to. We are so efficient at killing off germs that now we have left ourselves vulnerable. I say let's get a little dirtier!
If you are looking to learn more about this, try reading the pithy Parasitology Research Trends (Advances in Biology and Medicine)