Cystoisospora belli, formerly known as Isospora belli, is a parasite that can infect the intestines of humans. This parasite is typically found in tropical and subtropical regions, where poor sanitation and hygiene practices can contribute to its spread. Infection with Cystoisospora belli can cause symptoms such as diarrhea, abdominal pain, and weight loss, particularly in individuals with weakened immune systems. It is important for healthcare providers to be aware of this parasite and its potential impact on human health in order to properly diagnose and treat infected individuals.

Through this article, you’ll be able to answer the following questions:

• What disease does Cystoisospora belli cause?
• What are the characteristics of Cystoisospora belli?
• What is another name for Cystoisospora belli?
• What are the hosts of Cystoisospora belli?
• What is the life cycle of Cystoisospora belli?
• What is the morphology of the Cystoisospora belli?

Classification

• Domain: Eukaryota
• Kingdom: Chromista
• Phylum: Apicomplexa
• Class: Conoidasida
• Order: Eucoccidiorida
• Family: Sarcocystidae
• Genus: Cystoisospora
• Species: C. belli

Morphology

Oocysts

• Oocysts are formed by the union of microgametes and macrogametes, resulting in infective oocytes.
• The oocyst of Cystoisospora belli is oval and transparent, ranging in size from 25 to 35µm long by 10–15µm wide, with an average of 30 by 12µm.
• The developing morphologic form within the oocyst is known as a sporoblast, which consists of a roundish, immature sac that contains a small, discrete nucleus and granular cytoplasm.
• As the sporoblast matures, the young oocyst divides into two sporoblasts. These two sporoblasts continue to mature until they become sporocysts.
• Sporocyst consist of a mature, roundish sac containing four sausage-shaped sporozoites.
• This stage is known as the mature oocyst, and throughout its development, the sporoblast and sporocysts are surrounded by a colorless, smooth, two-layered cell wall.

Figure 1 Left (Unsporulated oocyst of C. belli. 20 µm.), Right (Sporulated oocyst of C. belli. 20 µm)

Life Cycle of Cystoisospora belli

• Cystoisospora belli is the only known coccidian parasite that does not have intermediate hosts. Humans are the only known definitive hosts and have no known animal reservoir.
• Infection starts with the ingestion of the infective sporulated oocyst in fecally contaminated beverages or food.
• The oocyst needs at least 1-2 days outside the host in order to sporulate and become infectious to a new host.
• Direct transmission from person to person is thought not to occur. There are four sporozoites residing within each of the two sporocysts contained by the oocyst.
• Four sporozoites reside within each of the two sporocysts contained by the oocyst.
• Digestion of the cyst walls causes the release of the sporozoites into the lumen of the small intestine, where they enter columnar epithelial cells.
• Asexual reproduction follows, which leads to an increased number of merozoites.
• Cystoisosporiasis in humans is similar to the sexual phase of Toxoplasma gondii in cats.
• Sometimes, gametocytes develop, resulting in the production of an oocyst, and oocysts are passed in the fecal mass unsporulated and are non-infectious. As earlier mentioned, the oocysts require 1-2 days to sporulate after reaching the external environment.
• In immunocompromised patients (HIV/AIDS), the parasite can invade and reproduce in other organs such as the liver, spleen, lymph nodes, and gall bladder.

Figure 2 Life Cycle of Cystoisospora belli

Pathogenicity

• Cystoisospora belli causes protracted, secretory diarrhea in AIDS patients with low CD4+ T cell counts.
• In patients suffering from other varieties of immunosuppression, the disease resembles that induced by Cryptosporidium.
• In most immunocompetent patient populations, infection is either subclinical or the diarrhea is transitory.
• Malabsorption of fats in immunocompromised patients has been reported.

Clinical Disease (Signs, symptoms, causes)

• Common symptoms include fever, abdominal cramping, diarrhea, malaise, and weight loss.
• In immunocompetent patients with HIV/AIDS, symptoms include watery, non-bloody diarrhea, malabsorption with steatorrhea, vomiting, foul-smelling stools, and dehydration.
• Complications such as death resulting from wasting associated with protracted weight loss and electrolyte imbalance may occur. However, symptoms usually resolve with specific treatment of the infection or reconstitution of the immune system with highly active antiretroviral therapy (HAART).

Diagnosis

• Cystoisospora belli, together with Dientamoeba fragilis and Sarcocystis spp., are the few protozoan pathogens that cause peripheral blood eosinophilia, and this can serve as indicators in the differential diagnosis of a patient with diarrhea.
• A definitive diagnosis is made through the identification of the unsporulated oocysts by microscopy in a stool sample.
• Another sample used for the diagnosis and identification of Cystoisospora belli are duodenal aspirates and small intestinal tissues in heavy infections, which often reveal intracellular parasites.

Treatment

• Trimethoprim-sulfamethoxazole is the treatment of choice and is used as a prophylaxis in HIV-infected individuals, along with HAART.
• Alternative treatments include pyrimethamine and nitazoxanide, while ciprofloxacin is a second line, though less effective.

Prevention and Control

• Water, hygiene, and sanitation are important for controlling the spread of the disease.
• Prophylaxis consists of avoiding contamination of food and drink with human feces.
• Proper disposal of human feces

Conclusion

In conclusion, Cystoisospora belli is a protozoan parasite that primarily infects the small intestine of humans. It is commonly found in areas with poor sanitation and is a leading cause of diarrhea in immunocompromised individuals. However, it should be noted that while Cystoisospora belli can cause diarrhea in immunocompromised individuals, it typically does not cause severe illness in healthy individuals with a normal immune system. Additionally, Cystoisospora belli can be transmitted through the ingestion of contaminated food or water, making proper hygiene practices crucial in preventing its spread. 

Workshop

One of the easiest ways of identifying Cystoisospora belli is by collecting stool samples from an HIV patient suffering from diarrhea and observing them under the microscope using the various diagnosis methods.

References

• Parasitic Diseases / Dickson D. Despommier, Robert W. Gwadz, Daniel O. Griffin, Peter J. Hotez, Charles A. Knirsch: – 6th edition, P. 177,  Protozoa of Minor Medical Importance. Cystoisospora belli (Formerly known as Isospora belli)
• Parasitology for Medical and Clinical Laboratory Professionals by Ridley, John W. Ridley (z-lib.org).Chapter 3, P 70 
• Textbook of Medical Parasitology © 2007, CK Jayaram Paniker, P 104
• Clinical Parasitology A PRACTICAL APPROACH, Second Edition, Elizabeth A. Gockel-Blessing (formerly Zeibig), PhD, MLS(ASCP)CM P. 165, CHAPTER 7
• https://en.wikipedia.org/wiki/Cystoisospora_belli
• Garcia, L. (2006). “Isospora belli“. Waterborne Pathogens. Denver: American Water Works Association. pp. 217–9. ISBN 978-1-58321-403-9.