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Cystoisosporiasis Treatment & Management

  • Author: Venkat R Minnaganti, MD, FACP; Chief Editor: Michael Stuart Bronze, MD  more...
Updated: Dec 02, 2015

Approach Considerations

In immunocompetent patients, cystoisosporiasis is a mild protracted illness. In patients with AIDS, patients with malignancy, or in patients undergoing chemotherapy, cystoisosporiasis can be debilitating or life-threatening. Hemorrhagic colitis occurs in rare cases.

Consultation with an infectious diseases specialist, a gastroenterologist, or both may be appropriate. Only patients with chronic cystoisosporiasis associated with severe dehydration should require continued inpatient care. Transfer may be required for the required specialists and/or therapeutic measures, if not available at the current institution.

Although cystoisosporiasis is generally a self-limited infection, patients who are treated tend to improve in 2-3 days, whereas those who are not treated remain sick considerably longer.

Immunocompetent hosts generally respond very rapidly to antiparasitic therapy, with symptomatic improvement within 5 days. Immunocompromised hosts also respond well, though less rapidly. However, these individuals relapse at a high rate (50% in 2 mo) once therapy is stopped. Such patients (eg, those with AIDS) may need life-long suppressive treatment with trimethoprim-sulfamethoxazole (TMP-SMZ).


Supportive Care

Care is supportive and symptomatic. Antibiotics may be administered (see Pharmacologic Therapy). Fluid replacement and correction of electrolyte imbalance are helpful. Therapy for dehydration may be the most urgent intervention required. Fluid losses may range from 2-20 L/d. Patients with severe diarrhea may require hospitalization.

No specific diet is recommended in patients with isosporiasis, but a low-protein, lactose-free diet is advised until any diarrhea has resolved.


Pharmacologic Therapy

For cystoisosporiasis, unlike many of the protozoal infections that cause similar diseases, effective therapies are available.

Cystoisosporiasis does not respond well to most antibiotics used to treat diarrhea. TMP-SMZ is the drug of choice because it is the best-studied and most readily available agent. Many patients with AIDS are already taking this agent as prophylaxis for Pneumocystis infection. One case report of isosporiasis refractory to TMP-SMZ has been described.[8]

Oral TMP-SMZ is well absorbed, even in patients with enteritis. A combination of 160 mg of TMP with 800 mg of SMZ (1 double-strength tablet PO q6h for 2-4 wk) is the preferred regimen. In patients who are intolerant to sulfonamides, pyrimethamine (50-75 mg PO q24h) with folinic acid (5-10 mg PO q24h) may be given for 2-4 weeks.

Patients with AIDS may require maintenance therapy for long-term suppression of C belli, typically in the form of 1 TMP-SMZ double-strength tablet 3 times a week. An alternative for long-term prophylaxis is pyrimethamine with sulfadiazine or sulfadoxine (eg, pyrimethamine 25 mg with sulfadoxine 500 mg 3 times a week), either of which should be accompanied by folinic acid. For patients who cannot tolerate sulfonamides, ciprofloxacin or pyrimethamine plus folinic acid may be nearly as effective for  treatment of an acute episode and for prophylaxis.

Studies have proposed the veterinary agent diclazuril as a possible drug of choice if further investigation confirms its use and safety.[9] Doxycycline, roxithromycin, and nitazoxanide[10, 11] are reported to have some efficacy, but the clinical data available are insufficient to recommend their routine use at present.

Anecdotal case reports also document improvement with albendazole, bismuth subsalicylate, furazolidone, metronidazole, and quinacrine; again, however, clinical trials are lacking.



Cystoisosporiasis is a food-borne and water-borne illness. Consequently, the practice of hygienic measures may help in preventing transmission. It is important to avoid possible exposure to contaminated food and water insofar as is possible.

Appropriate isolation measures should be used because shedding of oocysts may last for weeks.

Contributor Information and Disclosures

Venkat R Minnaganti, MD, FACP Consulting Staff, Department of Medicine, Winthrop University Hospital; Clinical Instructor, Department of Internal Medicine, Division of Infectious Disease, SUNY Stony Brook University School of Medicine

Venkat R Minnaganti, MD, FACP is a member of the following medical societies: All India Ophthalmological Society, American College of Physicians, American Medical Association, American Society for Microbiology, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

John W King, MD Professor of Medicine, Chief, Section of Infectious Diseases, Director, Viral Therapeutics Clinics for Hepatitis, Louisiana State University Health Sciences Center; Consultant in Infectious Diseases, Overton Brooks Veterans Affairs Medical Center

John W King, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Federation for Medical Research, Association of Subspecialty Professors, American Society for Microbiology, Infectious Diseases Society of America, Sigma Xi

Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Association, Oklahoma State Medical Association, Southern Society for Clinical Investigation, Association of Professors of Medicine, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

Klaus-Dieter Lessnau, MD, FCCP Clinical Associate Professor of Medicine, New York University School of Medicine; Medical Director, Pulmonary Physiology Laboratory; Director of Research in Pulmonary Medicine, Department of Medicine, Section of Pulmonary Medicine, Lenox Hill Hospital

Klaus-Dieter Lessnau, MD, FCCP is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Medical Association, American Thoracic Society, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Glenn Fennelly, MD, MPH Director, Division of Infectious Diseases, Lewis M Fraad Department of Pediatrics, Jacobi Medical Center; Clinical Associate Professor of Pediatrics, Albert Einstein College of Medicine

Glenn Fennelly, MD, MPH is a member of the following medical societies: Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

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Oocyst of Cystoisospora belli with 2 sporoblasts. From the Image Library, Division of Parasitic Diseases at the National Center for Infectious Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia.
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