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At time of excretion,
the immature oocyst contains usually one sporoblast (more rarely two)
.
In further maturation after excretion, the sporoblast divides in two (the
oocyst now contains two sporoblasts); the sporoblasts secrete a cyst wall,
thus becoming sporocysts; and the sporocysts divide twice to produce four
sporozoites each
.
Infection occurs by ingestion of sporocysts-containing oocysts: the
sporocysts excyst in the small intestine and release their sporozoites,
which invade the epithelial cells and initiate schizogony
.
Upon rupture of the schizonts, the merozoites are released, invade new
epithelial cells, and continue the cycle of asexual multiplication
.
Trophozoites develop into schizonts which contain multiple merozoites.
After a minimum of one week, the sexual stage begins with the development of
male and female gametocytes
.
Fertilization results in the development of oocysts that are excreted in the
stool
.
Isospora belli infects both humans and animals.
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