Introduction Isospora belli History of Discovery Transmission Clinical Presentation Treatment Web Links References

Isospora belli

Isosporiasis is caused by the protozoan Isospora belli. I. belli is also classified as a coccidia, a suborder characterized by unicellular intestinal parasites. The general term for the intestinal disease caused by coccidia is coccidiosis (2).

Kingdom: Protozoa
Subkingdom: Biciliata
Infrakingdom: Alveolata

Phylum: Myzozoa
Subphylum: Apicomplexa

Class: Conoidasida
Subclass: Coccidiasina

Order: Eucoccidiorida
Suborder: Eimeriorina

Family: Eimeriidae

Genus: Isospora

Species: belli (7)

Morphology and Life Cycle

Oocysts (the stage of I. belli that exists in the external environment) are ovoid in shape and measure 20-33 x 10-19 µm.

Life cycle of Isospora belli (individual figures from 1, 4, 6)

1) Immature, unsporulated oocyst is excreted through feces.
2) Sporoblast divides into two.
3) Each sporoblast develops into a sporocyst with 4 sporozoites, resulting in mature oocysts. The time spent in stages 1 through 3 is 2-3 days.
4) Mature oocyst is ingested.
5) Oocyst bursts. Sporozoites are released and lodge into the intestinal lining. Sporozoites undergo asexual reproduction to form merozoites. The merozoites mature into gametes which undergo fertilization to produce a new oocyst. (3)