eMedicine Specialties > Infectious Diseases > Parasitic Infections

Isosporiasis

Author: Venkat R Minnaganti, MD, Consulting Staff, Department of Medicine, Winthrop University Hospital; Clinical Instructor, Department of Internal Medicine, Division of Infectious Disease, State University of New York School of Medicine at Stony Brook
Contributor Information and Disclosures

Updated: Oct 24, 2008

Introduction

Background

Isosporiasis is an uncommon diarrheal illness caused by the protozoan Isospora belli. Humans are the only known hosts for I belli, which has no known animal reservoir. Isosporiasis has a worldwide distribution, although it is more common in tropical and subtropical climates. In 1860, Virchow first described Isospora. In 1915, the first case of human infection with I belli was described.1 The genus Isospora is related closely to the genera Cryptosporidium, Cyclospora, and Toxoplasma.

Pathophysiology

The oocysts of I belli are resistant and remain viable in the environment for months. Ingestion of mature I belli oocysts leads to invasion of the epithelial cells of the distal duodenum and proximal jejunum, with resulting cell damage. Symptoms of isosporiasis suggest a toxin-mediated mechanism, but no toxin has been identified. In humans, extraintestinal forms of isosporiasis are rare but have been reported in patients with AIDS.

Frequency

United States

The exact incidence of isosporiasis in humans is unknown. I belli has been reported as the cause of outbreaks of diarrheal illness in daycare centers and mental institutions and has been implicated in traveler's diarrhea in endemic areas.2

Isosporiasis is more common in persons with AIDS, but this increased prevalence has been mollified by the widespread use of Pneumocystis jiroveci pneumonia (PCP) prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMZ) among patients with HIV infection. Isosporiasis is an initial AIDS-defining illness in approximately 0.2% of patients with AIDS. Isosporiasis has also been reported in patients with lymphoma and leukemia and recipients of renal and liver transplants.

International

Endemic areas of isosporiasis include Africa, Australia, the Caribbean Islands, Latin America, and Southeast Asia.

Isosporiasis is the initial AIDS-defining illness in approximately 2-3% of patients with AIDS who are from Africa. Among patients with AIDS who are from South America, 10% with chronic diarrhea have isosporiasis. In patients with AIDS who are from Haiti and Africa, 7-20% with chronic diarrhea have isosporiasis.

Mortality/Morbidity

In immunocompetent patients, isosporiasis is usually a transient illness but can result in a protracted diarrheal illness. Isosporiasis has also been reported as a contributor to malabsorption syndrome in immunocompetent patients.3

In patients with AIDS, isosporiasis can vary from a chronic and intermittent illness to a severe and life-threatening diarrheal illness.

Race

Among patients with AIDS, isosporiasis is more prevalent in Hispanics than in blacks or whites.

Sex

Males and females are equally susceptible to isosporiasis.

Age

I belli can infect both adults and children and can cause severe diarrhea in infants. For information on pediatric isosporiasis, see the eMedicine article Isosporiasis in the Pediatrics: General Medicine volume.

Clinical

History

The mode of transmission of isosporiasis is fecal-oral, ie, through food or water contaminated with human feces. I belli infection usually causes a mild and protracted illness unless the patient is immunocompromised.

  • The incubation period ranges from 3-14 days.
  • Symptoms and signs include the following:
    • Profuse, watery, nonbloody, offensive-smelling diarrhea, which may contain mucus
    • Cramping abdominal pain, vomiting
    • Malaise, anorexia, weight loss
    • Low-grade fever
    • Steatorrhea in protracted cases

Causes

  • I belli infection causes isosporiasis.
  • Isosporiasis is more common in areas with poor sanitation.
  • The disease is also more common in patient with AIDS.

More on Isosporiasis

Overview: Isosporiasis
Differential Diagnoses & Workup: Isosporiasis
Treatment & Medication: Isosporiasis
Follow-up: Isosporiasis
Multimedia: Isosporiasis
References
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Further Reading

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Keywords

isosporiasis, Isospora belli, I belli, Isospora belli infection, I belli infection, extraintestinal isosporiasis, disseminated isosporiasis, intestinal parasitic infections, Isospora belli enteritis, I belli enteritis, Cryptosporidium, Cyclospora, Toxoplasma

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Contributor Information and Disclosures

Author

Venkat R Minnaganti, MD, Consulting Staff, Department of Medicine, Winthrop University Hospital; Clinical Instructor, Department of Internal Medicine, Division of Infectious Disease, State University of New York School of Medicine at Stony Brook
Venkat R Minnaganti, MD is a member of the following medical societies: All India Ophthalmological Society, American College of Physicians, American Medical Association, American Society for Microbiology, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Medical Editor

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 Society for Artificial Internal Organs, American Thoracic Society, Physicians for Social Responsibility, and Society of Critical Care Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

John W King, MD, Professor of Medicine, Section of Infectious Diseases, Louisiana State University Health Sciences Center; Director, Viral Therapeutics Clinics for Hepatitis; Consulting Staff, Department of Infectious Diseases, Overton Brook 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, American Society for Microbiology, Association of Subspecialty Professors, Infectious Diseases Society of America, and Sigma Xi
Disclosure: emedicine $50.00 author of chapter

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD, Professor, Stewart G Wolf Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center
Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physician Executives, American College of Physicians, American College of Physicians-American Society of Internal Medicine, American Federation for Clinical Research, American Medical Association, American Society for Microbiology, Association of Professors of Medicine, Association of Program Directors in Internal Medicine, Infectious Diseases Society of America, Oklahoma State Medical Association, and Southern Society for Clinical Investigation
Disclosure: Nothing to disclose.

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