The coccidia (sporozoa) are non-motile parasites that belong to the phylum Apicomplexa. This group of organisms have unique organelles that make up an apical complex, which allow them to enter into cells. They have more complex life cycles than the other organisms discussed so far and can alternate between sexual and asexual reproduction. A famous member of this group of parasites is the genus Plasmodium, which causes malaria.
The apicomplexan parasites belonging to the genera, Cryptosporidium, Cystoisospora, and Cyclospora, all develop exclusively in the vertebrate intestinal tract, whereas Sarcocystis can have an extraintestinal phase.
As mentioned above, they alternate between sexual and asexual reproduction, developing into several different stages. Some the stages of sporozoan life cycles include:
- The sporozoite is the stage that emerges from the oocyst and enters the intestinal epithelial cell.
- The trophozoite develops from the merozoite and can grow and reproduce asexually to form merozoites. These forms can enter more intestinal cells or develop into microgametes and macrogamonts which fuse to form zygotes.
- Zygotes can divide further then to give rise to the sporozoites which develop in the oocyst.
