Official reprint from UpToDate®
www.uptodate.com ©2017 UpToDate, Inc. and/or its affiliates. All Rights Reserved.

Epidemiology, clinical manifestations, and diagnosis of Cystoisospora (Isospora) infections

Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
Section Editor
Peter F Weller, MD, MACP
Deputy Editor
Jennifer Mitty, MD, MPH


Cystoisospora belli (formerly known as Isospora belli) is a gastrointestinal protozoan. In patients with AIDS and other immunodeficiencies, it is an opportunistic pathogen that can cause watery diarrhea and weight loss. Like other enteric pathogens such as Cryptosporidium and Cyclospora, C. belli is a coccidian, unicellular protozoan parasite that primarily infects the intestinal epithelium [1].


Cystoisospora belli is found worldwide, but infections are more common in tropical and subtropical areas [2]. In India, Cystoisospora infections are the most common parasitic cause of diarrhea in HIV-infected subjects [3,4]. Among HIV-infected patients living in France, Cystoisospora infections were seen more commonly among patients who had emigrated from sub-Saharan Africa [5].

Gastrointestinal infections secondary to Cystoisospora are uncommon in the United States, but can be acquired by travelers to endemic countries [6-9]. In a study of more than 16,000 HIV-infected patients between 1985 and 1992 in Los Angeles County, the prevalence of Cystoisospora infections was highest in foreign-born patients, particularly those from Mexico and El Salvador, and among persons of Hispanic ethnicity [6]. Cystoisospora can also be identified as a copathogen with other enteric organisms, such as Enterocytozoon bieneusi, in geographic regions with high levels of fecal contamination of surface water [10].

In contrast, a history of treatment or prophylaxis with trimethoprim-sulfamethoxazole for Pneumocystis infection in an HIV-infected patient is associated with a decreased risk of developing cystoisosporiasis [6,11].

Cystoisospora has also been reported in immunocompetent patients as well as in patients with other cellular immunodeficiencies, such as human T-lymphotropic type 1 infection [12], lymphoblastic leukemia, adult T-cell leukemia, Hodgkin's disease, and non-Hodgkin lymphoma [13]. It has also been reported in patients taking immunomodulators such as TNF-inhibitors [14].

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:

Subscribers log in here

Literature review current through: Nov 2017. | This topic last updated: Apr 25, 2017.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2017 UpToDate, Inc.
  1. Goodgame RW. Understanding intestinal spore-forming protozoa: cryptosporidia, microsporidia, isospora, and cyclospora. Ann Intern Med 1996; 124:429.
  2. www.dpd.cdc.gov/dpdx/html/cystoisosporiasis.htm (Accessed on December 19, 2011).
  3. Vignesh R, Balakrishnan P, Shankar EM, et al. High proportion of isosporiasis among HIV-infected patients with diarrhea in southern India. Am J Trop Med Hyg 2007; 77:823.
  4. Gupta S, Narang S, Nunavath V, Singh S. Chronic diarrhoea in HIV patients: prevalence of coccidian parasites. Indian J Med Microbiol 2008; 26:172.
  5. Lagrange-Xélot M, Porcher R, Sarfati C, et al. Isosporiasis in patients with HIV infection in the highly active antiretroviral therapy era in France. HIV Med 2008; 9:126.
  6. Sorvillo FJ, Lieb LE, Seidel J, et al. Epidemiology of isosporiasis among persons with acquired immunodeficiency syndrome in Los Angeles County. Am J Trop Med Hyg 1995; 53:656.
  7. DeHovitz JA, Pape JW, Boncy M, Johnson WD Jr. Clinical manifestations and therapy of Isospora belli infection in patients with the acquired immunodeficiency syndrome. N Engl J Med 1986; 315:87.
  8. Shaffer N, Moore L. Chronic travelers' diarrhea in a normal host due to Isospora belli. J Infect Dis 1989; 159:596.
  9. Goodgame R. Emerging Causes of Traveler's Diarrhea: Cryptosporidium, Cyclospora, Isospora, and Microsporidia. Curr Infect Dis Rep 2003; 5:66.
  10. Raccurt CP, Fouché B, Agnamey P, et al. Presence of Enterocytozoon bieneusi associated with intestinal coccidia in patients with chronic diarrhea visiting an HIV center in Haiti. Am J Trop Med Hyg 2008; 79:579.
  11. Guiguet M, Furco A, Tattevin P, et al. HIV-associated Isospora belli infection: incidence and risk factors in the French Hospital Database on HIV. HIV Med 2007; 8:124.
  12. Greenberg SJ, Davey MP, Zierdt WS, Waldmann TA. Isospora belli enteric infection in patients with human T-cell leukemia virus type I-associated adult T-cell leukemia. Am J Med 1988; 85:435.
  13. Resiere D, Vantelon JM, Bourée P, et al. Isospora belli infection in a patient with non-Hodgkin's lymphoma. Clin Microbiol Infect 2003; 9:1065.
  14. Stein J, Tannich E, Hartmann F. An unusual complication in ulcerative colitis during treatment with azathioprine and infliximab: Isospora belli as 'Casus belli'. BMJ Case Rep 2013; 2013.
  15. Forthal DN, Guest SS. Isospora belli enteritis in three homosexual men. Am J Trop Med Hyg 1984; 33:1060.
  16. Ryan ET, Cronin CG, Branda JA. Case records of the Massachusetts General Hospital. Case 38-2011. A 34-year-old man with diarrhea and weakness. N Engl J Med 2011; 365:2306.
  17. Jongwutiwes S, Putaporntip C, Charoenkorn M, et al. Morphologic and molecular characterization of Isospora belli oocysts from patients in Thailand. Am J Trop Med Hyg 2007; 77:107.
  18. Benator DA, French AL, Beaudet LM, et al. Isospora belli infection associated with acalculous cholecystitis in a patient with AIDS. Ann Intern Med 1994; 121:663.
  19. Takahashi H, Falk GA, Cruise M, Morris-Stiff G. Chronic cholecystitis with Cystoisospora belli in an immunocompetent patient. BMJ Case Rep 2015; 2015.
  20. González-Dominguez J, Roldán R, Villanueva JL, et al. Isospora belli reactive arthritis in a patient with AIDS. Ann Rheum Dis 1994; 53:618.
  21. Gellin BG, Soave R. Coccidian infections in AIDS. Toxoplasmosis, cryptosporidiosis, and isosporiasis. Med Clin North Am 1992; 76:205.
  22. Pape JW, Verdier RI, Johnson WD Jr. Treatment and prophylaxis of Isospora belli infection in patients with the acquired immunodeficiency syndrome. N Engl J Med 1989; 320:1044.
  23. Restrepo C, Macher AM, Radany EH. Disseminated extraintestinal isosporiasis in a patient with acquired immune deficiency syndrome. Am J Clin Pathol 1987; 87:536.
  24. Panel on Opportunistic Infections in HIV-Infected Adults and Adolescents. Guidelines for the prevention and treatment of opportunistic infections in HIV-infected adults and adolescents: Recommendations from the Centers for Disease Control and Prevention, the National Institutes of Health, and the HIV Medicine Association of the Infectious Diseases Society of America http://aidsinfo.nih.gov/contentfiles/lvguidelines/adult_oi.pdf (Accessed on July 22, 2013).
  25. Berlin OG, Conteas CN, Sowerby TM. Detection of Isospora in the stools of AIDS patients using a new rapid autofluorescence technique. AIDS 1996; 10:442.
  26. Bialek R, Binder N, Dietz K, et al. Comparison of autofluorescence and iodine staining for detection of Isospora belli in feces. Am J Trop Med Hyg 2002; 67:304.
  27. Ribes JA, Seabolt JP, Overman SB. Point prevalence of Cryptosporidium, Cyclospora, and Isospora infections in patients being evaluated for diarrhea. Am J Clin Pathol 2004; 122:28.
  28. ten Hove RJ, van Lieshout L, Brienen EA, et al. Real-time polymerase chain reaction for detection of Isospora belli in stool samples. Diagn Microbiol Infect Dis 2008; 61:280.
  29. Sun T, Ilardi CF, Asnis D, et al. Light and electron microscopic identification of Cyclospora species in the small intestine. Evidence of the presence of asexual life cycle in human host. Am J Clin Pathol 1996; 105:216.