The term parasitism may be defined as a two-species association in which one species, the parasite, lives on or in a second species, the host, for a significant period of its life and obtains nourishment from it. This is a commonly accepted working definition of parasitism and using it we can emphasize several important features of the host-parasite relationship. Parasitism always involves two species, the parasite and the host. Many of these parasitic associations produce pathological changes in hosts that may result in disease. Successful treatment and control of parasitic diseases requires not only comprehensive information about the parasite itself but also a good understanding of the nature of parasites' interactions with their hosts. The parasite is always the beneficiary and the host is always the provider in any host-parasite relationship.
This definition of parasitism is a general one but it tells us nothing about parasites themselves. It does not address which particular infectious organisms of domestic animals we might include in the realm of parasitology. The protozoa, arthropods and helminths are traditionally defined as parasites. However, there are members of the scientific community who designate all infectious agents of animals as parasites including viruses, protozoa, bacteria and fungi as well as the arthropods, helminths and protozoa. Within this broad definition, parasites are further divided into microparasites and macroparasites. The following subsections summarizes the common parasites of birds.
|Sarcocystis spp||Atoxoplasma spp|