The genus Eimeria are apicomplexan parasites which affect domestic mammals and birds. All Eimeria are species-specific. In chickens, infection with one or more species of Eimeria can cause the enteric disease, coccidiosis. There are seven species of Eimeria known to infect chickens and differ in pathogenicity. These include E. acervulina, E. brunetti, E. maxima, E. tenella, E. necatrix, E. praecox, and E. mitis. Each species of Eimeria have a preference for a specific location in the bird's gastrointestinal tract.
Life Cycle: The Eimeria life cycle consists of two basic stages---the exogenous phase (sporogony) and the endogenous phase (schizogony and gametogony). Eimeria begins as an infective sporozoite, found in sporulated oocysts which are what the chickens initially ingest. Once inside the bird, they travel through their digestive system until they reach their preferred spot. At the preferred location, the sporozoites are released from the oocysts where they begin to infect the intestinal cells where they transition into a trophozoite.
Survival in the Environment: Sporulated Eimeria oocysts are resistant to adverse environmental conditions and can survive as long as one year in moist, protected environments if they are not exposed to freezing or extremely high temperatures.