Fig. 2.

Life cycle of Eimeria tenella. Numbers correlate with subsequent stages of the development. (1) Oocyst sporulation in the environment and oral ingestion by the chicken. (2) Release of sporocysts and sporozoites along the transit in the chicken digestive system. (3) Active invasion of sporozoites in the ceaeca epithelium and formation of the intracellular trophozoite within the parasitophorous vacuole. (4) First round of shyzogony and release of first generation merozoites. (5) Second and third rounds of shyzogony and release of second and third generation merozoites, respectively. (6) Development of microgametes and macrogametes (gametogony) and fecundation. (7) Zygote, development of the oocyst and release to the environment as unsporulated oocyst.