Eimeria stiedae

Eimeria spp. have a one host life cycle in vertebrates, with both sexual and asexual reproduction occurring. The parasite lives and multiplies intracellularly, infecting epithelial cells. Hosts are infected by oocyst ingestion. Most species infect the intestine, but Eimeria stiedae infects the bile duct epithelium of rabbits. An oocyst containing four sporozoites isingested by the rabbit. The sporozoites break out of the oocyst and travel to the bile duct,where they penetrate the epithelial cells. Within the epithelial cell they undergo an asexual multiplication process called schizogony, in which a schizont is formed that eventually forms many merozoites. The merozoites rupture the host cell and individual merozoites penetrate a new epithelial cell. One or more rounds of schizogony may ensue. Eventually a merozoite will entera new epithelial cell and begin the sexual portion of the life cycle. Some merozoites will become microgametocytes ("male") while others will become macrogametes ("female"). The microgametocyte will divide asexually to produce many microgametes which break out of the host cell. The microgametes must then penetrate a cell containing a macrogamete, and fertilize it, producing a zygote. A wall forms around the zygote to become the oocyst. The oocyst breaks free of the infected cell and passes down the digestive tract and is expelled in the faeces. Once outside, the zygote within the oocyst sporulates, forming four sporozoites, and is then infective to another rabbit. In your slides, which are tissue sections, you should be able to see many zygotes and oocysts, as well as some schizonts. If lucky you may be able to find some gametocytes. The following images are of a different species of Eimeria than found in your slide box. However, the life cycle pattern and the overall morphology are similar.

The following images are taken from slide transparencies produced by Dr. S. S. Desser, University of Toronto, Toronto Canada.

Eimeria tenella unsporulated oocyst

Eimeria tenella sporulated oocyst

Eimeria tenella merozoites in schizonts

Eimeria tenella merozoites

Eimeria tenella microgametocytes and macrogametocyte

Eimeria tenella macrogametocytes

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