Date of this Version
Coccidia are exceptionally common protist parasites of both vertebrates and, to a lesser extent, invertebrates. Every vertebrate species that ever has been examined intensively, over a broad geographic range, has been found to have at least one coccidian species unique to it and may have as many as five, ten, or more species. They also may have additional coccidia shared with close relatives (congenerics, sometimes confarnilials) and/or with sympatrics. The history of the development of our knowledge about coccidian parasites of wild mammals is long and tangled and has been reviewed by Levine, Joyner, and Long and Joyner. Suffice it to say that the coccidia were among the very first protozoans ever visualized when Antonie van Leeuwenhoek saw what surely were the oocysts of Eimeria stiedai in the bile of a rabbit in 1674.
In this review, we limit our coverage to the coccidia of wild mammals that have direct (homoxenous) life cycles; reproduce both asexually (merogony) and sexually (gamogony) within the epithelial or endothelial cells of the gastrointestinal tract or related structures (e.g., bile duct, renal tubular epithelium, etc.) of their host; and produce as an end product, a resistant propagule, the oocyst, which leaves the host, usually via the feces. By far, the majority of coccidia with these characteristics are placed taxonomically into four genera contained in two families: Eimeriidae (Cyclospora, Eimeria, Isospora) and Cryptosporidiidae (Cryptosporidium). The taxonomy of the coccidia is reviewed.