Isosporiasis

KEY FEATURES

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

  • Cystoisospora (formerly 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

• C belli appears to infect only humans

• Incubation period for C 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

CLINICAL FINDINGS

Symptoms and Signs

In immunocompetent patients

• 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

DIAGNOSIS

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 aspirates or small bowel biopsy specimens

TREATMENT

Medications

• Most infections in immunocompetent persons do not require treatment

• Trimethoprim-sulfamethoxazole

  • 160 mg/800 mg orally 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 orally daily)

• 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

OUTCOME

Complications