ABSTRACT
The typical Coccidian life cycle pattern consists of three developmental phases: sporogony, schizogony, and gamogony (Fig. 1). Different morphological types result from each developmental phase; sporozoites from sporogony, merozoites from schizogony, and zygotes from gamogony. The only diploid stage in the life cycle is the zygote. Following meiosis, the zygote becomes a multinucleate sporont and undergoes multiple fission (sporogony). Depending on the species, the haploid cells formed are either free infective sporozoites or sporozoites enclosed within an oocyst or spore, from which they subsequently escape. Within the host, infective sporozoites become intra-or extracellular vegetative trophozoites. The trophozoites develop first into multinucleate schizonts, which then undergo multiple fission (schizogony) producing numerous daughter cells or merozoites. Merozoites either continue the infection of the host with repetition o f asexual multiplication and invasion of other host cells, or they develop into sexual stages termed gamonts. Gamonts undergo multiple fission (gamogony) and give rise to gametes. The latter join in pairs in syngamy to produce diploid zygotes.
