Cystoisospora belli - Introduction, Classification, Morphology, Epidemiology, Transmission

Introduction of Cystoisospora belli

Cystoisospora belli, previously known as Isospora belli, causes an infection of the gastrointestinal tract called cystoisosporiasis. They mostly cause infection in immune-suppressed human hosts. This opportunistic parasitic coccidian is closely related to the genus Cryptosporidium, Cyclospora, and Toxoplasma.

Classification of Cystoisospora belli

Phenotypically, Cystoisospora belli is classified as:

Kingdom: Chromista

Superphylum: Alveolata

Phylum: Apicomplexa

Class: Conoidasida

Order: Eucoccidiorida

Family: Sarcocystidae

Genus: Cystoisospora

Species: C. belli

History of Cystoisospora belli

Historically, Cystoisospora belli was first described in 1860 by Virchow. The first case of known human infection was described in 1915 among military personnel in World War. This protozoan parasite was named in 1923 by Wenyon.

Habitat of Cystoisospora belli

Cystoisospora belli habitats and infect the epithelial cells of the small intestine and develops in the cell cytoplasm.

In the natural environment, the parasite is cosmopolitan but is mainly found in tropical and subtropical areas of the world such as the Caribbean, Central, and South America, India, Africa, and South East Asia.

Morphology of Cystoisospora belli

Morphologically, Cystoisospora belli exists in the following steps:

Diagnostic form in humans

Oocysts

• Cystoisospora belli oocysts is found in humans

• diagnostic form of Cystoisospora belli

• elliptical shape but may vary in shape from long to slender or short

• measures 20 μm to 33 μm x 10μm to 19 μm

• each oocyst contains two sporoblasts and is surrounded by a two-layered cyst wall

• each sporoblast has four sporozoites

• these sporozoites are slender, long, and crescent-shaped

• sporozoites remain in a cluster of four within the sporocyst wall which also contains granular residual mass

Infective form

Oocyst containing two sporoblasts

• the infective form of Cystoisospora belli is an oocyst containing two sporoblasts

• immature oocyst are excreted

• immature oocysts contain mostly one sporoblast (rarely two)

• these oocysts mature outside the host

• maturation of oocyst includes the formation of two sporoblasts with each containing four sporozoites

Epidemiology of Cystoisospora belli

Cystoisospora belli is worldwide in distribution but is more common in tropical and subtropical climates.

The infection is endemic to Latin America, Australia, the Caribbean islands, Africa, Southeast Asia, etc.

Reservoir, Source of Cystoisospora belli

Infected hosts are the reservoir/source of infection and no animal reservoir has been found.

Mature oocysts are the infective stages of Cystoisospora belli.

Transmission of Cystoisospora belli

Transmission of Cystoisospora belli occurs through the fecal-oral route- through water or food contaminated with oocysts.