Isosporiasis

Essentials of Diagnosis

IN IMMUNOCOMPETENT PATIENTS

• Self-limited watery diarrhea lasting 2–3 weeks

• Abdominal cramps, anorexia, malaise, weight loss

• Fever is unusual

IN IMMUNOCOMPROMISED PATIENTS

• Severe and chronic diarrhea

• Extraintestinal disease has been reported rarely

General Considerations

• Causes of coccidiosis

  • Cryptosporidium spp, particularly C parvum and C hominis

  • Isospora belli

  • Cyclospora cayetanensis

  • Sarcocystis species

• These organisms cause endemic childhood gastroenteritis (particularly in malnourished children in developing countries)

• Infection is transmitted from person to person or by contaminated drinking or swimming water or food

• Ingested oocysts release sporozoites that invade and multiply in enterocytes, primarily in the small bowel

• Coccidian oocysts and microsporidian cysts can remain viable in the environment for years

• I belli appears to infect only humans

• Incubation period for I belli is about 1 week

Demographics

• The infection occurs worldwide, particularly in the tropics and in regions where hygiene is poor

• Clustering occurs in households, day care centers, and among sexual partners

Symptoms and Signs

IN IMMUNOCOMPETENT PERSONS

• Causes a self-limited watery diarrhea lasting 2–3 weeks

• Abdominal cramps, anorexia, malaise, and weight loss

• Fever is unusual

• Chronic symptoms may persist for months

IN IMMUNOCOMPROMISED PATIENTS

• Causes severe and chronic diarrhea

• Extraintestinal disease has been reported rarely

Differential Diagnosis

• C parvum, I belli, S bovihominis, and S suihominis

• Giardiasis

• Viral gastroenteritis, eg, rotavirus

• Other traveler's diarrhea, eg, Escherichia coli

• Cholera

• Other causes of diarrhea in AIDS, eg, cytomegalovirus colitis

Laboratory Tests

• Diagnosis is made by examination of stool wet mounts or after modified acid-fast staining, in which the organism is clearly distinguishable from other parasites

• Other stains also show the organism

• Sensitivity of stool evaluation is not high because shedding of oocysts may be intermittent; multiple samples should be examined

Diagnostic Procedures

• Organism may also be identified in duodenal aspiration or small bowel biopsy specimens

Medications

• Most infections in immunocompetent persons do not require treatment

• Trimethoprim-sulfamethoxazole

  • 160 mg/800 mg two to four times daily for 10 days

  • Higher doses for patients with AIDS

• An alternative therapy is pyrimethamine (75 mg orally in four divided doses) with folinic acid (10–25 mg/day orally)

• Maintenance therapy prevents relapse in persons with persistent immunosuppression

  • Low-dose trimethoprim-sulfamethoxazole (160 mg/800 mg daily or three times per week)

  • Fansidar (1 tablet weekly)

Therapeutic Procedures

• Supportive treatment for severe or chronic diarrhea includes

  • Fluid and electrolyte replacement

  • Parenteral nutrition

Complications

• Marked dehydration, malnutrition, and hemorrhagic colitis in immunocompromised patients

Prevention

• Water purification is important for control of these infections

• Chlorine disinfection is not effective against cryptosporidial oocysts, so other purification measures are needed

• Immunocompromised patients should

  • Boil or filter drinking water

  • Consider avoiding lakes and swimming pools

• Routine precautions (handwashing, gloves, disinfection) should prevent institutional patient-to-patient spread

When to Refer

• Persistent symptoms despite therapy, particularly in immunocompromised patients

When to Admit

• Profuse diarrhea causing hypotension or electrolyte imbalance