Cystoisosporiasis is an intestinal illness that results from the protozoan parasite Cystoisospora belli that was previously called Isospora belli. Cystoisospora belli is an apicomplexan protozoan. It is coccidian parasite which is mainly located in the intestinal system. Infection is mainly through the oral route where the organism’s oocysts are passed in the feces of infected persons. These oocysts may be found in food and water, and on surfaces that meet the feces of infected animals and humans. It transmits from animals to humans by poor sanitation and hygiene practices such as consumption of contaminated food and water. 

The prevalence of cystoisosporiasis in the United States is undefined, however; Cystoisospora belli has been associated with diarrheal episode in childcare centers and has been identified in traveler’s diarrhea in areas where the disease is endemic. This infection is rather not frequent in most individuals who have intact immune system, but it is frequent in AIDS patients: 0.2 to 3% testing positive. 

C. belli antibodies were detected in 1% of AIDS patients seen between 1985 and 1992 in Los Angeles, with higher expression in the foreign-born and Hispanic population. It is also found in cancer patients and in organ transplant recipients though it may affect patients with normal or near normal immunity.

Globally, Cystoisospora belli is reported in Africa, Australia, Caribbean, Latin, America, Southeast Asia and other parts of the world. In these regions, up to 15% of Haitians with AIDS test positive for the HIV, and 8 to 40% of AIDS patients in developing nations are infected. It is found to be the first AIDS defining disease in 2 to 3% of AIDS patients in Africa; 7 to 20% of patients who have cystoisosporiasis experience chronic diarrhea in Haiti and Africa. 

Cystoisospora belli can infect anyone, but it commonly affects children and is more severe in infants since it causes severe dehydration. There is no preference of the infection with either the male or female gender or race, but Hispanics with AIDS in the U. S. are riskier probably due to geographical influence.

Cystoisospora belli is acquired through consumption of contaminated food or water and undergoes part of its life cycle outside the host. Mature C.belli oocysts are ingested and the sporozoites are released, this can be initiated by bile in the small intestine and penetrate enterocytes in the proximal small intestine. In its host cells, sporozoites transform into trophozoites, and multiply through schizogony into merozoites, which invade other cells. 

This is followed by the sexual reproduction phase (sporogony), and leads to formation of new oocysts, which are then released into the environment. They are ingested with food and mature extra-intestinal and turn infectious in 2 to 3 days. C. belli oocysts are resistant, and this fact was proved by the results of studies where the oocysts were found to be stable in the environment and capable of infecting humans after several months. 

Though signs of isosporiasis point to toxin-induced disease, such toxin has not been discovered. Systemic manifestations of cystoisosporiasis are rare in human diseases but have been reported in AIDS patients. 

The infection is acquired through the fecal-oral route, which involves consuming food or water contaminated with human feces. In healthy immunocompetent hosts, it causes relatively mild and self-limited diarrhea. However, in immunocompromised individuals they may lead to persistent severe diarrhea and therefore dehydration. 

The transmission of the pathogen is directly related to the consumption of contaminated food or water. Because the parasite is only released as oocysts which need adequate environmental conditions to develop further outside of the host, direct human to human transmission is a rarity. Therefore, isosporiasis is more frequent in areas with poor standard of hygiene and it is more frequent in people with AIDS. 

In immunocompetent hosts, cystoisosporiasis is usually an acute self-limiting illness though can present with chronic diarrhea in some instances. There have also been cases some of which showed that cystoisosporiasis could have caused malabsorption syndrome in these patients. 

In those with AIDS, cystoisosporiasis may range from chronic, subacute to an acute fulfilment form of diarrhoeal illness. 

Age Group 

• All ages: Cystoisosporiasis may develop in people of any age, but it is more often identified in adults. 
• Immunocompromised Individuals: Especially, it is common in the patients with the immunocompromised condition like the patients with HIV/AIDS. 

Dehydration: Cracked and pale lips, rough and sticky surface of the tongue, skin elasticity is low, eyes are sunken. 

Abdominal Exam: Tenderness should be mild especially in lower part of abdomen; high pitch bowel sounds. 

Nutritional Status: Weight loss, in severe stages, could be associated with loss of muscle mass. 

Vital Signs: Tachycardia and possible hypotension resulting from dehydration. 

Malabsorption syndrome

HIV/AIDS 

Immunocompetent Individuals: Generally, begins with the sudden appearance of watery diarrheal which is often mild and usually resolves without medical intervention. Nonetheless, it occasionally offers a more extensive diarrheal disease process. 

Immunocompromised Individuals: It can also be chronic and may repeatedly relapse cause severe dehydration and malnutrition. In AIDS patients for instance, the illness may escalate into a critical stage and become fatal if not well handled. 

Antimicrobial Therapy: 

Trimethoprim-Sulfamethoxazole (TMP-SMX): 

• First-line treatment: TMP-SMX is the drug of choice in pregnant women. Normally, TMP is 160 mg and SMX is in 800 mg, with a double strength given twice daily for 7-10 days for the healthy individuals. 
• For Immunocompromised Patients: The courses can be longer, frequently taking 10-14 days or more and chronic suppressive therapy may be needed to avoid a relapse. 

Alternative Therapy: 

• Pyrimethamine: For patients with an intolerance to TMP-SMX, pyrimethamine can be used together with folinic acid to minimize side effects. 
• Ciprofloxacin: Is employed as an alternative to TMP-SMX although is less beneficial compared to TMP-SMX. 
• Rehydration: Sodium bicarbonate for patients with moderate to severe cases of acidosis and hypertension Oral rehydration solutions or intravenous fluids for patients with moderate to severe cases of dehydration and electrolyte imbalances. 
• Nutritional Support: Some of the key immunosuppressants included are: Ensuring the patient is adequately nourishing especially when the patient has lost a lot of weight or was malnourished. 

Secondary Prophylaxis in AIDS Patients: 

• TMP-SMX: TMP-SMX thrice weekly or daily for those who have high chance of the shots recurring. 
• Alternative Regimens: TMP-SMX should be given with caution to patients with renal and hepatic impairment. One may consider using pyrimethamine with folinic acid or ciprofloxacin in patients who cannot tolerate TMP-SMX. 

Management of Underlying Conditions: 

HIV/AIDS Management: 

• Antiretroviral Therapy (ART): Short-term ART that enhances immunity to contain ailments that progress at the background of a compromised immune system. 
• General Immunosuppression: Supervising and controlling the doses of immunosuppressive medicines in clients with other diseases such as transplants to prevent the attack of diseases. 

Public Health Measures: 

• Sanitation and Hygiene: Optimal measures needed to enhance food hygiene and water quality to avoid the transmission of fecal-oral route diseases. 
• Education: Raising awareness about the aspects of personal and mass hygiene measures like washing hands, preparing foods, and consuming water. 

Infectious Disease

Hydration: 

• Oral Rehydration Therapy (ORT): To avoid dehydration, especially when diarrhea is persistent, you should use the oral rehydration solutions. This is important in balancing the electrolytes in the body as well as keeping the consistency of bones, tissues, teeth and joints. 
• Intravenous Fluids: There are times a patient may require intravenous interventions if they are severely dehydrated through replenishing of fluids along with necessary electrolytes. 
• Nutritional Support: Promote a diet which is high in calories and composed of nutrient dense foods in preparation for compensating for any nutrient that may have been lost through diarrhea or that may not be being absorbed appropriately. Having small and frequent meals also helps in maintaining the energy levels and at the same time avoiding a load on the digestion system. 
• Probiotics: Since the infection is likely to interfere with the normal bacterial flora in the gut, intake of probiotics may assist in replenishing the good bacteria. They may help to tone up the gut and may help to shorten duration of diarrhoea. 

Infectious Disease

Trimethoprim-Sulfamethoxazole (TMP-SMX): TMP-SMX belongs to the group of drugs that exert their effects through the blockade of biosynthesis of dihydrofolic acid required for bacteria proliferation. This is widely recommended treatment, and it has been known to cure cystoisosporiasis in ordinary individuals who have normal functioning immune systems. In immunocompromised patients, it can be administered for primary therapy as well as chronic secondary prophylaxis. 

Pyrimethamine (Daraprim): This is due to its property of being a folic acid antagonist it competes with dihydrofolate reductase in parasites of the malaria. It is used in the management of patients who cannot take sulfonamides. It may be used together with sulfadiazine or sulfadoxine, mainly for preventive purposes. Due to the facilitated destruction of the hematopoietic elements, it should be accompanied by folinic acid. 

Diclazuril: Status-Allowed as an investigational drug in the United States. The only 2-aminobenzene acetonitrile derivative is the Diclazuril which is mainly used for veterinary medicine as aromatic antiparasitic. Minimal research has been done with human subjects which points to that it is safe and is effective. It has been used mainly in veterinary medicine, but its efficacy in clinical trials to treat the diarrheal effects of the cryptosporidium in AIDS patients has been relatively good.

Infectious Disease

Leucovorin: It belongs to folic acid, which is used in conjunction with folic acid inhibitors such as sulphonamides and pyrimethamine. 

Infectious Disease

Intravenous Fluid Administration: In patients with severe diarrheal disease with dehydration, IV fluids are used to replenish the fluid and electrolyte loss rapidly. This intervention is essential especially among the patients to avoid some of the complications associated with dehydration. 

Nutritional Support: Weight loss and malnutrition shall be treated through changes in diet and possibly through enteral feedings if necessary due to inadequate oral intake. This way the patient is assured of getting the necessary calories and nutrients that they require when in the process of recovery. 

Endoscopic Evaluation: Endoscopy is not usually performed but it may be used for investigation of complications or where there is a need to determine the degree of damage to the intestine as well as to exclude other diseases in patients who present more severe or persistent signs. 

Infectious Disease

The management of the cystoisosporiasis has been understood to contain the following important phases. It is first diagnosed clinically and then confirmed through a stool examination or molecular test. Management in the acute setting involves the prescription of TMP-SMX or other antibiotics if necessary and the provision of fluids and nutrition. During the prophylactic phase, TMP-SMX is continued for maintenance to prevent relapse in immunocompromised patients, and patients are followed-ups closely for any sign of relapse. Proper health management measures that can help in the prevention are to teach patients about measures to take to avoid getting in contact with infected water and there is always the need to ensure that water is properly treated.