There are many different possible strategies for the parasite to follow. Some have one host whereas others have multiple hosts. Some use intermediate hosts for transport. The host may live or be killed by the parasite. Sometimes the host is spare, but the parasite eliminates the host's reproductive abilities.
Parasites can be bacteria, fungi, protozoa, arthropods or helminths.
They can cause a number of medical, veterinary and agricultural problems. Examples include amoebic dysentery, giardiasis, toxoplasmosis , pinworm and scabies. It has been estimated that parasitism in more common than all other forms of disease. It is a major problem in third world countries. Also included are links to a number of parasitology lecture courses, sites with lots of images and other cool sites.