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Salem Health: Infectious Diseases & Conditions, 2nd Edition

Isosporiasis

by Katia Marazova, , M.D., Ph.D.

Category: Diseases and conditions

Anatomy or system affected: Abdomen, gastrointestinal system, intestines

Definition

Isosporiasis is an uncommon human parasitic infection of the intestines characterized by profuse watery diarrhea and cramping abdominal pain.

Causes

Isosporiasis is caused by the coccidian protozoan parasite Isospora belli (taxonomically related to Cryptosporidium, Cyclospora, and Toxoplasma species), which infects the epithelial cells of the small intestine. Humans are the only known host for this parasite. Infection is typically acquired by the ingestion of oocysts in food or water contaminated with the feces of infected humans (fecal-oral mode of transmission).

Risk Factors

Isosporiasis has a worldwide distribution but is more common in tropical and subtropical regions, particularly in areas with poor sanitation. Endemic areas include Africa, Australia, the Caribbean Islands, Latin America, and Southeast Asia. Males and females are equally susceptible to isosporiasis. The disease can affect both adults and children and can cause severe diarrhea in infants. The exact prevalence of isosporiasis is unknown.

Isosporiasis is more common in persons with acquired immunodeficiency syndrome (AIDS). Reports suggest infection rates of up to 3 percent in persons with AIDS in the United States and of 8 to 20 percent in persons with AIDS in Haiti and Africa; these rates, however, may be underestimated. Isosporiasis has also been reported in persons with lymphoma and leukemia and in recipients of renal and liver transplants.

Symptoms

The incubation period ranges from three to fourteen days. Clinical manifestations may include a variety of symptoms, including profuse diarrhea with watery, nonbloody, foamy, mucus-containing, offensive-smelling diarrhea (suggestive of a malabsorption process); cramping abdominal pain; vomiting; malaise; anorexia; weight loss; and low-grade fever. In protracted cases, steatorrhea (an excess of fat in the feces) may occur. Clinical presentation may mimic inflammatory bowel disease and irritable bowel syndrome. Complications are rare and include dehydration, hemorrhagic colitis, and disseminated extraintestinal disease.

In immunocompetent persons, the disease is usually self-limiting within two to three weeks. Occasionally, chronic illness occurs in infants or in otherwise healthy adults. In persons with immune dysfunction, especially AIDS, isosporiasis can persist for months and years, or it can persist indefinitely and can be a life-threatening diarrheal illness.

Screening and Diagnosis

Diagnosis is made by appropriate staining techniques and by microscopic examination of the stool specimen for ova. Routine laboratory tests are not diagnostic. However, peripheral eosinophilia may be a clue to infection because mild peripheral eosinophilia is found in one-half of infected persons.

Treatment and Therapy

Oral cotrimoxazole (sulfamethoxazole at 800 milligrams [mg] and trimethoprim at 160 mg) is the drug of choice (four times daily for one to four weeks). This treatment ameliorates the diarrhea and eliminates the parasite in majority of cases. In persons who cannot take sulfonamides, pyrimethamine with folinic acid or ciprofloxacin may be used. Persons with AIDS who develop isosporiasis may need lifelong suppressive treatment with cotrimoxazole. Only those persons with chronic isosporiasis that is associated with severe dehydration should require continued inpatient care.

Prevention and Outcomes

Because isosporiasis is typically spread by ingesting contaminated food or water, preventive measures include improved personal hygiene and sanitation to eliminate possible fecal-oral transmission from food, water, and environmental surfaces. Appropriate isolation measures may help in preventing transmission because the shedding of oocysts may last for weeks.

Further Reading

1 

Farthing, Michael J. G. “Treatment Options for the Eradication of Intestinal Protozoa.” Nature Clinical Practice Gastroenterology and Hepatology 3 (2006): 436-445.

2 

Goodgame, Richard W. “Understanding Intestinal Spore-Forming Protozoa: Cryptosporidia, Microsporidia, Isospora, and Cyclospora.” Annals of Internal Medicine 124 (1996): 429-441.

3 

Marshall, M. M., et al. “Waterborne Protozoan Pathogens.” Clinical Microbiology Reviews 10 (1997): 67-85.

4 

Minnaganti, Venkat R. “Isosporiasis.” Available at http://emedicine.medscape.com/article/219776-overview.

5 

Ortega, Ynes. “Food- and Waterborne Protozoan Parasites.” In Foodborne Pathogens: Microbiology and Molecular Biology, edited by Pina M. Fratamico, Arun K. Bhunia, and James L. Smith. Norwich, England: Caister Academic Press, 2005.

Web Sites of Interest

American Gastroenterological Association

http://www.gastro.org

Global Health Council

http://www.globalhealth.org/infectious_diseases

U.S. Department of Agriculture: Food Safety and Inspection Service

http://www.fsis.usda.gov

See also: Amebic dysentery; Antiparasitic drugs: Types; Cryptosporidiosis; Diagnosis of protozoan diseases; Enteritis; Fecal-oral route of transmission; Food-borne illness and disease; Giardia; Giardiasis; Intestinal and stomach infections; Norovirus infection; Parasitic diseases; Peritonitis; Prevention of protozoan diseases; Protozoa: Classification and types; protozoan diseases; Sexually transmitted diseases (STDs); Soilborne illness and disease; Treatment of protozoan diseases; Waterborne illness and disease.

Citation Types

Type
Format
MLA 9th
Marazova, Katia. "Isosporiasis." Salem Health: Infectious Diseases & Conditions, 2nd Edition, edited by H. Bradford Hawley, Salem Press, 2020. Salem Online, online.salempress.com/articleDetails.do?articleName=Infect2e_0315.
APA 7th
Marazova, K. (2020). Isosporiasis. In H. B. Hawley (Ed.), Salem Health: Infectious Diseases & Conditions, 2nd Edition. Salem Press. online.salempress.com.
CMOS 17th
Marazova, Katia. "Isosporiasis." Edited by H. Bradford Hawley. Salem Health: Infectious Diseases & Conditions, 2nd Edition. Hackensack: Salem Press, 2020. Accessed September 16, 2025. online.salempress.com.