Not Found

Find information on medical topics, symptoms, drugs, procedures, news and more, written for the health care professional.

* This is the Professional Version. *

Cyclosporiasis and Cystoisosporiasis

By Richard D. Pearson, MD, University of Virginia School of Medicine

Click here for
Patient Education

Cyclosporiasis is infection with Cyclospora cayetanensis; cystoisosporiasis is infection with Cystoisospora (Isospora) belli Both organisms are coccidian protozoa. Symptoms include watery diarrhea with GI and systemic symptoms. Diagnosis is by detection of characteristic oocysts in stool or intestinal biopsy specimens. Treatment is usually with trimethoprim/sulfamethoxazole.

The life cycles of C. cayetanensis and C. belli are similar to that of Cryptosporidium, except that oocysts must sporulate before becoming infective. Human cyclosporiasis and cystoisosporiasis are most common in tropical and subtropical climates. Transmission is by the fecal-oral route via contaminated food or drink. In the 1990s, outbreaks of C. cayetanensis in North America were caused by ingestion of raspberries imported from Guatemala. In the summer of 2013, a multistate outbreak involving hundreds of people in the US was attributed to ingestion of prewashed salad mixes.

Symptoms and Signs

The primary symptom is sudden, nonbloody, watery diarrhea, with fever, abdominal cramps, nausea, anorexia, malaise, and weight loss. In immunocompetent patients, the illness usually resolves spontaneously but can last weeks.

In hosts with depressed cell-mediated immunity as occurs in AIDS, cyclosporiasis and cystoisosporiasis may cause severe, intractable, voluminous diarrhea resembling cryptosporidiosis. Extraintestinal disease in patients with AIDS may include cholecystitis and disseminated infection.


  • Microscopic examination of stool

Diagnosis is by detection of oocysts via microscopic examination of the stool. Detection is facilitated by staining stool samples with modified acid-fast stain or modified safranin stain. Multiple (≥ 3) stool specimens may be needed because cyst secretion may be intermittent. Diagnosis is sometimes made only when intracellular parasite stages are detected in biopsies of intestinal tissue. In cystoisosporiasis, cysts autofluoresce when ultraviolet microscopy is used; the stool may contain Charcot-Leyden crystals (hexagonal, double-pointed, and often needlelike crystals) derived from eosinophils. Unlike other protozoan infections, cystoisosporiasis may result in peripheral blood eosinophilia.


  • Trimethoprim/sulfamethoxazole

Treatment of choice for both cyclosporiasis and cystoisosporiasis is double-strength trimethoprim/sulfamethoxazole (TMP/SMX): 160 mg TMP and 800 mg SMX po bid for 7 to 10 days for cyclosporiasis or for 10 days for cystoisosporiasis. Children are given 5 mg/kg TMP and 25 mg/kg SMX po bid for the same number of days.

In patients with AIDS, higher doses and longer duration may be needed, and treatment of acute infection is usually followed by long-term suppressive therapy. Institution or optimization of antiretroviral therapy (ART) is important.

For cyclosporiasis, an alternative to TMP/SMX has yet to be identified.

Ciprofloxacin 500 mg po bid for 7 days has been used to treat cystoisosporiasis, but it is less effective than TMP/SMX.

Prevention is as for cryptosporidiosis (see Cryptosporidiosis : Prevention).

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • No US brand name

* This is the Professional Version. *