page_title: Cystoisospora belli
section_title: Life cycle
hierarchical_section_title: Cystoisospora belli / Life cycle
caption_attribution_description: ID#:3398 This is an illustration of the life cycle of Isospora belli, the causal agent of Isosporiasis. At time of excretion, the immature oocyst contains usually one sporoblast (more rarely two) (1). 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 (2). 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 (3). Upon rupture of the schizonts, the merozoites are released, invade new epithelial cells, and continue the cycle of asexual multiplication (4). 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 (5). Fertilization results in the development of oocysts that are excreted in the stool (1). Isospora belli infects both humans and animals. ([1])
context_page_description: Cystoisospora belli, previously known as Isospora belli, is a parasite that causes an intestinal disease known as cystoisosporiasis. This protozoan parasite is opportunistic in immune suppressed human hosts. It primarily exists in the epithelial cells of the small intestine, and develops in the cell cytoplasm. The distribution of this coccidian parasite is cosmopolitan, but is mainly found in tropical and subtropical areas of the world such as the Caribbean, Central and S. America, India, Africa, and S.E. Asia. In the U.S., it is usually associated with HIV infection and institutional living.
context_section_description: An oocyst with one sporoblast is released in stool of infected person
  After the oocyst has been released, the sporoblast matures further and divides into two
  After the sporoblasts divide they create a cyst wall and become sporocysts
  The sporocysts each divide twice, resulting in four sporozoites
  Transmission occurs when these mature oocysts are ingested
  The sporocysts excyst in the small intestine where sporozoites are released
  The sporozoites then invade epithelial cells and schizogony  is initiated
  When the schizonts rupture, merozoites are released and continue to invade more epithelial cells
  Trophozoites develop into schizonts, containing many merozoites
  After about one week, development of male and female gametocytes begin in the merozoites
  Fertilization results in the development of oocysts, which are released in the stool 
  The sporulation time of this parasite's egg is usually 1–4 days, and the entire life cycle takes about 9–10 days. The infective stage found in stool is the mature oocyst. The mature oocyst for Cystoisospora belli can remain infective in the environment for months.
caption: PHIL 3398 lores
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