What are the other Names for this Condition? (Also known as/Synonyms)

• Cystoisospora Belli Infection 
• Isospora Belli Infection
• Isosporiasis

What is Cystoisosporiasis? (Definition/Background Information)

• Cystoisosporiasis is a disease caused by infection of the small intestine by a protozoan parasite that is transmitted fecal-orally through contaminated food and water. It is found worldwide, most commonly in resource-limited tropical and subtropical countries with poor sanitation conditions
• Cystoisosporiasis is caused by a tiny parasite called Cystoisospora belli (formerly Isospora belli), which can be seen under a microscope. The infection was formerly known as Isosporiasis. Infection is acquired by ingesting food or water contaminated with the infective form of the parasite i.e., the sporulated oocysts, which are formed by the maturation of oocysts passed in the feces of infected individuals
• The freshly passed oocysts are not infective and take 1-10 days to mature (sporulate) depending on the environmental conditions. Therefore, direct person-to-person transmission and transmission via freshly contaminated food or water do not occur
• Cystoisosporiasis is characterized by watery diarrhea. Abdominal pain, loss of appetite, nausea, weakness, fever, and weight loss are some other symptoms associated with the condition. The illness is usually mild and self-limited in individuals with healthy immune systems
• However, those with weak immunity, such as HIV positive individuals, are at an elevated risk of developing severe prolonged diarrhea and extra-intestinal manifestations (e.g., chronic acalculous cholecystitis)
• Stool samples over several days are analysed to detect the presence of the parasite to arrive at a definite diagnosis. The various diagnostic tests for Cystoisosporiasis include microscopic identification of parasite and polymerase chain reaction, to detect the protozoan genetic material
• Cystoisosporiasis is typically treated using antibiotics. Rest and plenty of fluids are prescribed to maintain hydration. Severe cases may require hospitalization too. In most individuals with healthy immunity, the prognosis of the condition is excellent
• The main method of preventing Cystoisosporiasis is to avoid consuming contaminated food and water. Thorough hand washing, thoroughly washing raw vegetables and fruits, using clean water for drinking, and cooking food to proper temperatures can help reduce the chances of contracting the infection

Who gets Cystoisosporiasis? (Age and Sex Distribution)

• Cystoisosporiasis occurs worldwide, but most commonly in certain economically weaker tropical and subtropical countries where hygiene and sanitation conditions are poor
• The infection affects individuals of all age groups and both male and female genders

In the United States, it occurs as foodborne outbreaks and infection in those traveling to the endemic countries.

What are the Risk Factors for Cystoisosporiasis? (Predisposing Factors)

The following are some of the risk factors for Cystoisosporiasis:

• Individuals living in or traveling to the endemic areas
• Drinking contaminated or impure water
• Consumption of imported fresh produce without washing them
• Eating raw fruits and vegetables without washing

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one's chance of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Cystoisosporiasis? (Etiology)

Cystoisosporiasis is caused by infection of the small intestine by the parasite Cystoisospora belli, a tiny coccidian parasite visible only under a microscope.

• Infection occurs from ingestion of food or water contaminated with feces of infected individuals. The infective form of the parasite is the sporulated oocyst which is the mature oocyst containing sporozoites
• The ingested sporulated oocysts release sporozoites which invade the lining of the small intestine. The sporozoites develop and multiply in the intestine and produce immature oocysts which are passed in the feces of infected individuals. In around one week after infection, the oocysts start shedding in the feces

The freshly passed oocysts are not infective and take 1-10 days to mature and sporulate (develop sporozoites inside) to become infective. Therefore, direct human-to-human transmission and transmission via freshly contaminated food or water are less likely to occur.

What are the Signs and Symptoms of Cystoisosporiasis?

Cystoisosporiasis most commonly presents with watery, non-bloody diarrhea 2-14 days (average 7 days) after ingesting the mature oocysts of Cystoisospora belli.

• The following are the other signs and symptoms that may be exhibited:
  • Loss of appetite
  • Weight loss
  • Stomach cramps/pain
  • Bloating and gas
  • Nausea and vomiting
  • Fatigue (extreme tiredness)
  • Dehydration
  • Slight fever
• If Cystoisosporiasis is not treated, the infection can persist and cause continuous or intermittent symptoms for weeks and months
• Individuals with weak immunity, such as HIV positive individuals, are at elevated risk of developing severe prolonged diarrhea and biliary disease (e.g., acalculous cholecystitis), which can potentially be fatal if not treated adequately

How is Cystoisosporiasis Diagnosed?

To make a diagnosis of Cystoisosporiasis, it is important to have a high index of suspicion and collect information about the signs and symptoms, conduct a physical examination, evaluate history of travel to endemic regions, and suspected consumption of contaminated food/water.

• The healthcare provider may need to make a specific request to test for Cystoisospora belli
• Multiple stool samples over several days may need to be tested
• Aspirate or biopsy tissue from the small intestine may also be used to detect the parasite, if stool examination results are inconclusive
• One distinctive feature which is not seen in other coccidian parasite infections is the presence of peripheral eosinophilia (increased number of eosinophils in blood)

Stool specimens are tested using different techniques such as:

• Microscopy: 
  • The typically shaped oocysts of Cystoisospora belli can be identified on microscopy
  • Different staining and microscopy techniques can be used to make the oocysts more prominent for identification
• Molecular methods: Polymerase chain reaction (PCR) test to detect the genetic material of the parasite

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Cystoisosporiasis?

Individuals at elevated risk of developing complications are those with immunosuppressive conditions such as:

• HIV infection and AIDS
• Prolonged steroid intake
• Individuals on treatment with immunosuppressive medications (such as transplant recipients)
• Cancers, including leukemia, lymphoma, thymoma, among others
• Other immunodeficiency disorders

In an HIV-positive individual, Cystoisosporiasis persisting for more than one month in duration is an “AIDS-defining illness” i.e., it is one of the diagnostic indicators that HIV infection has progressed to the advanced stage known as AIDS.

The complications that may arise directly from Cystoisosporiasis include:

• Severe dehydration 
• Severe malnutrition
• Profound weight loss
• Gallbladder and biliary tract infection such as chronic acalculous cholecystitis

How is Cystoisosporiasis Treated?

Cystoisosporiasis is typically treated with a course of antibiotics. The affected individuals are advised to take rest and plenty of fluids to prevent dehydration.

• Additionally, the following measures may be considered:
  • Fluid and electrolyte replacement therapy - either oral or intravenous replacement may be done to treat dehydration
  • Anti-motility medications may be used to slow the movement of the intestine and increase fluid and nutrient absorption. This can help reduce the risk of dehydration. However, these drugs should be taken only after consulting a healthcare provider
• Anti-retroviral therapy for HIV and AIDS patients: Highly-active anti-retroviral therapy (HAART) can help reduce the viral load in the body and boost the immune system

How can Cystoisosporiasis be Prevented?

There is no vaccine currently available for Cystoisosporiasis. Avoiding consuming contaminated food and water is the best available method to prevent infection.

The following measures may be helpful in reducing the risk of contracting the infection:

• Frequently washing hands with soap and water, especially after using toilet, changing diapers, and before eating, cooking, or handling food
• Thoroughly washing with clean water and peeling raw vegetables and fruits before consuming them. Fruits and vegetables labelled ‘prewashed’ do not need to be washed again at home
• Avoid eating raw fruits and vegetables, especially imported ones; cooking the fruits and vegetables prior to consuming them (especially in the endemic areas)
• Washing utensils and food preparation surfaces with soap and hot water after preparing food
• Avoiding the use of untreated water for drinking purposes in endemic areas. Using bottled water for drinking, mouth washing, cooking, or washing of fresh produce to be eaten raw, if filtered (clean) water is not available

Note:

• A routine chemical disinfection of water is unlikely to kill Cystoisospora belli, since it is highly resistant to chlorine
• It is important to teach children the importance of hand washing and the proper method to wash their hands

What is the Prognosis of Cystoisosporiasis? (Outcomes/Resolutions)

• In individuals with healthy immune systems, Cystoisosporiasis resolves itself after a few days of diarrhea. In some untreated individuals, the infection can persist longer and cause recurrent episodes of diarrhea
• Individuals with weak immunity due to various factors, or those who have HIV infection, may develop severe prolonged diarrhea and biliary disease that could potentially lead to death if not treated adequately

Additional and Relevant Useful Information for Cystoisosporiasis:

The following DoveMed website link is a useful resource for additional information:

https://www.dovemed.com/diseases-conditions/infection-center/

https://www.dovemed.com/diseases-conditions/cryptosporidiosis/