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What is Isospora Belli Infection: Causes, Symptoms, Treatment, Diagnosis

What Is Isospora Belli Infection?

Isospora Belli Infection which is also called by the name of Isosporiasis is a medical condition, which is caused by protozoa called Isospora belli with its main symptoms being diarrhea and other gastrointestinal symptoms. Isosporiasis (also known as Cystoisosporiasis) is an intestinal disease of humans caused by the coccidian parasite called Isospora belli (Cystoisospora belli). Isospora Belli Infection is a benign and self limiting condition and resolves on its own without treatment although if treatment is given then the recovery can be speeded up.

Isospora Belli Infection does not cause any complications, although people who get infected and have a compromised immune system may have complication of the infection spreading beyond the intestines to other parts of the body, especially people who are HIV positive and their viral load is not under control.

Isospora Belli Infection is quite rare and is spread through contaminated food and water. The parasite causing Isospora Belli Infection exists in an immature state in the environment until it enters the human body and gets mature in the intestines from where it gets infected. This usually occurs in the small intestines. Once the parasite gets infected, it infects the cells of the small intestine resulting in the typical symptoms of Isospora Belli Infection.

What Is Isospora Belli Infection?

What Causes Isospora Belli Infection?

As stated, Isospora Belli Infection is caused by ingesting contaminated food and water. which contains a parasite called Isospora belli. This is a rare parasite when compared to other infectious agents found in contaminated food and water causing illnesses. The immature form of the parasite is called as oocyte, which is ingested through contaminated food and water. Once inside the human body it matures to infect the small intestine.

Once the parasite completes its life cycle inside the human body, it is eliminated from the body through stool. The parasite that is eliminated through the feces may again contaminate water, which when ingested can cause Isospora Belli Infection again. An outbreak of Isospora Belli Infection can occur if a common water body, which is being used by large number of people for drinking purpose get contaminated. This is the reason why Isospora Belli Infection is very rare in most of the developed countries. Isospora Belli Infection is mostly found in areas where there is poor sanitation.

What Are The Symptoms Of Isospora Belli Infection?

Apart from severe diarrhea some of the other symptoms that are associated with Isospora Belli Infection are:

How To Diagnose Isospora Belli Infection?

Since Isospora Belli Infection is quite rare, hence its diagnosis is quite difficult and needs careful examination and various investigations. The most preferred method to diagnose Isospora Belli Infection is via stool cultures. Some of the other ways to diagnose Isospora Belli Infection is by collecting samples of intestinal fluids, which will be infected in case of Isospora Belli Infection, although collection of intestinal fluid is not always preferred. Blood tests are not done as it cannot conclusively diagnose Isospora Belli Infection.

What is the Treatment for Isospora Belli Infection?

As stated, Isospora Belli Infection is a benign self limiting condition and resolves on its own once the parasite is eliminated from the body in a normal individual with no abnormalities in the immune system. If treatment is given then the disease may be cured within a couple of days whereas it may take a couple of weeks for the symptoms to resolve without treatment. In people with compromised immune state, treatment is required as the disease may spread beyond the intestines and the symptoms are very severe and will show no signs of abating. For such individuals the most preferred treatment is with antibiotics and the medication used is trimethoprim-sulfamethoxazole to be used for about 10 days to about 3 weeks.

The patient is required to complete the course of the antibiotics even if there is an improvement of symptoms. In case if the above medication is not tolerated by the patient then pyrimethamine with folinic acid is recommended. The physician may also prescribe nutritional supplements to supplement any nutritional deficiencies that may arise due to prolonged illness.

Apart from medication, supportive care is also necessary for a speedy recovery. These supportive measures are aimed at preventing any dehydration due to prolonged diarrhea as a result of Isospora Belli Infection. The patient needs to be given oral rehydrating solutions constantly. If in case there is severe dehydration then treatment in an inpatient setting is required and the patient may need to stay in the hospital for a few days to recover from Isospora Belli Infection.


  1. Centers for Disease Control and Prevention (CDC) – Parasites – Cystoisosporiasis (Isosporiasis): https://www.cdc.gov/parasites/cystoisospora/index.html
  2. Medical Journal Armed Forces India – An Uncommon Cause of Chronic Diarrhea: Isospora Belli: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4211298/

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Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 1, 2023

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