eMedicine Specialties > Pediatrics: General Medicine > Parasitology

Isosporiasis

Author: Robert W Tolan Jr, MD, Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine
Contributor Information and Disclosures

Updated: Jan 22, 2009

Introduction

Background

First recognized as a human pathogen among military personnel during World War I, Isospora belli is an Apicomplexa coccidia protozoan that causes a self-limited diarrheal illness in immunocompetent hosts. In individuals with immunocompromise, it may cause chronic life-threatening diarrhea and dehydration.

Pathophysiology

I belli is ingested in contaminated food or water and its life cycle requires a stage outside the host. Oocysts liberate sporozoites (possibly in response to bile in the small intestine), which invade the enterocytes of the proximal small intestine. Here, they become trophozoites, and asexual multiplication (schizogony) produces merozoites that invade previously uninfected cells. Shortly thereafter, a sexual multiplication cycle (sporogony) begins, generating oocysts that may pass into the environment. Outside the host, oocysts mature and become infectious 2-3 days later. Oocysts may persist for months in the environment.

Frequency

United States

I belli infection is distinctly rare among immunocompetent individuals. Among patients with acquired immunodeficiency syndrome (AIDS), 0.2-3% have stools positive for Isospora. In Los Angeles from 1985-92, 1% of patients with AIDS had stools positive for Isospora.1 Infection was more common in foreign-born and Hispanic residents with AIDS (eg, those from El Salvador [7.4%] or Mexico [5.4%]) and less common in those receiving trimethoprim-sulfamethoxazole (TMP-SMZ) prophylaxis for Pneumocystis infection.1

International

Infection with Isospora is endemic in tropical regions, particularly of Central and South America, Africa, and Southeast Asia. One study found positive examination findings in up to 15% of Haitians infected with AIDS.2 In developing countries, 8-40% of patients with AIDS are infected.

Mortality/Morbidity

Generally a self-limited disease in immunocompetent hosts, I belli can cause chronic life-threatening diarrhea and dehydration, particularly in persons with AIDS.

Race

No racial predilection for isosporiasis has been reported, other than the racial distribution of people with AIDS. In the United States, Hispanics appear to be more at risk, likely secondary to importation.

Sex

No sex predilection for infection has been noted, aside from the sex distribution of people with AIDS, the risk factor most commonly associated with this disease.

Age

People of all ages are susceptible to this infection, although it tends to be more serious in infants and young children, possibly as a result of the risk of dehydration in this population.

Clinical

History

Typically, patients with isosporiasis present with mild crampy abdominal pain and profuse, watery, extremely foul-smelling diarrhea. I belli is most commonly observed in immunocompromised individuals or in individuals who have recently traveled to tropical areas, in people who are institutionalized, or in persons who live in poor sanitary conditions. Symptoms begin approximately 1 week after ingesting the oocysts and last 2-3 weeks, with gradual improvement. Infection in people who are immunocompromised may continue indefinitely.

  • Foul-smelling flatus may be reported.
  • Anorexia is sometimes reported.
  • Low-grade fever may be present.
  • Steatorrhea may occur.
  • Nausea and vomiting are uncommon.
  • Myalgias are rarely noted.
  • Headache is a rare symptom.

Physical

In immunocompromised individuals with severe or long-lasting disease, dehydration may be evident. Otherwise, minimal abdominal tenderness may be present.

Causes

Exposure to contaminated food or water predisposes to this infection. Because an external stage in the environment is required for the oocysts to mature, direct person-to-person transmission is unlikely.

More on Isosporiasis

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

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Further Reading

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Keywords

isosporiasis, Apicomplexa coccidia protozoan, dehydration, diarrhea, foul-smelling flatus, gastrointestinal infection, GI infection, Isospora, Isospora belli, I belli, I belli disease, I belli infection, parasitic infection, steatorrhea

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Contributor Information and Disclosures

Author

Robert W Tolan Jr, MD, Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine
Robert W Tolan Jr, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, Phi Beta Kappa, and Physicians for Social Responsibility
Disclosure: GlaxoSmithKline Honoraria Speaking and teaching; MedImmune Honoraria Consulting; MedImmune Honoraria Speaking and teaching; Merck Honoraria Speaking and teaching; Novartis Honoraria Speaking and teaching; sanofi pasteur Grant/research funds Unrestricted research grant; sanofi pasteur  Consulting; sanofi pasteur Honoraria Speaking and teaching; Tap Honoraria Speaking and teaching; Baxter Healthcare Honoraria Speaking and teaching

Medical Editor

Glenn J Fennelly, MD, MPH, Director, Division of Pediatric Infectious Diseases, Jacobi Medical Center; Associate Professor, Department of Pediatrics, Albert Einstein College of Medicine
Glenn J Fennelly, MD, MPH is a member of the following medical societies: Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from financial planner; Avanir Pharma Stock Investment from financial planner ; WebMD Salary and stock Employment and investment from financial planner

Managing Editor

Martin Weisse, MD, Program Director, Associate Professor, Department of Pediatrics, West Virginia University
Martin Weisse, MD is a member of the following medical societies: Ambulatory Pediatric Association, American Academy of Pediatrics, and Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.

CME Editor

Daniel Rauch, MD, FAAP, Director, Pediatric Hospitalist Program, Associate Professor, Department of Pediatrics, New York University School of Medicine
Daniel Rauch, MD, FAAP is a member of the following medical societies: Ambulatory Pediatric Association, American Academy of Pediatrics, and Society of Hospital Medicine
Disclosure: Baxter Honoraria Consulting; Pfizer Honoraria Consulting

Chief Editor

Russell W Steele, MD, Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine
Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, and Southern Medical Association
Disclosure: None None None

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