Enteroepithelial stages

The gametes contain the microgamete (the male gamete) and the macrogamete (the female gamete). The oocyst is the developed zygote which is a product of the sexual reproduction through the fertilization of the macrogamete by the microgamete. When excreted in cat faeces, the oocyst contains a sporont, which sporulates within 24-72h after excretion by dividing into two round masses called sporoblasts. The sporoblasts elongate and mature into sporocysts, and within each sporocyst four sporozoites develop. Thus the sporulated oocysts contain eight sporozoites.

Five morphologically distinct stages (types) of T. gondii develop in the intestinal epithelial cells before gametogony begins (Dubey and Frenkel 1972). With repeating nuclear division, merozoite formation starts with the development of an anterior membrane complex near the nucleus. Immature merozoites are formed when the new nuclei are included in the newly formed anterior membrane complex. The immature merozoites lie near the outer membrane of the mature meront. The outer membrane invaginates around each merozoite, and the now mature merozoites are released from the meront resulting in host cell death. Released mature merozoites initiate gametogony. The gamonts are found 315 days after infection in the ileum.

The macrogamete is sub-spherical and contains a single centrally located nucleus and several PASpositive granules (Ferguson et al. 1975).

During microgametogenesis the nucleus of the male gamonts divides to produce 10-21 nuclei. Each microgamete is biflagellate, appear laterally compressed, and has a large mitochodrium. Microgametes are fewer in number than macrogametes. The microgamete swims to the mature macrogamete, attach by the perforatorium, and penetrate the cell membrane, and we now have the fertilized gamete, the oocyst (Dubey and Frenkel 1972).

Oocyst wall formation is initiated by fertilization, and five layers are formed around the pellicle of the gamete (Ferguson et al. 1975). The oocysts are now discharged into the intestinal lumen by rupture of the epithelial cells. The mature, unsporulated oocyst, the sporont, is spherical and 10-12^m in diameter. The wall consists of two colourless layers, and the sporont almost fills the oocyst.

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