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Key Features

Essentials of Diagnosis

  • Acute diarrhea, especially in children in developing countries

  • Outbreaks of diarrhea secondary to contaminated water or food

  • Prolonged diarrhea in immunocompromised persons

  • Diagnosis mostly by identifying organisms in specially stained stool specimens

General Considerations

  • Infection occurs mainly by ingestion of spores, but also by direct inoculation of the eyes

  • May be transmitted from person to person or by contaminated drinking or swimming water or food

  • Cysts can remain viable in the environment for years


  • Occurs worldwide, particularly in the tropics and in regions where hygiene is poor

  • Clustering occurs in households, day care centers, and among sexual partners

Clinical Findings

Symptoms and Signs

In immunocompetent patients

  • Most commonly presents as self-limited diarrhea

  • Ocular infections have also been described

In immunocompromised patients

  • Most commonly caused by Enterocytozoon bieneusi and Encephalitozoon intestinalis

  • Chronic diarrhea, with anorexia, bloating, weight loss, and wasting

  • Fever is usually not seen

  • Other illnesses include

    • Biliary tract disease (AIDS cholangiopathy)

    • Genitourinary infection with cystitis

    • Kidney disease

    • Hepatitis

    • Peritonitis

    • Myositis

    • Respiratory infections including sinusitis

    • Central nervous system infections including granulomatous encephalitis

    • Disseminated infections

  • Ocular infections with Encephalitozoon species cause conjunctivitis and keratitis, presenting as redness, photophobia, and loss of visual acuity


Laboratory Findings

  • Identification of organisms in stool, fluid, or tissue specimens using Weber chromotrope-based stain

Diagnostic Studies

  • Electron microscopy is helpful for confirmation of the diagnosis and speciation

  • Polymerase chain reaction and culture techniques are available but not used routinely


  • Albendazole (400 mg orally twice daily for 2–4 weeks)

    • Has activity against a number of species, but relatively poor efficacy (about 50%) against E bieneusi, the most common microsporidial cause of diarrhea in AIDS patients

    • Used to treat gastrointestinal and other manifestations

  • Fumagillin

    • Has shown benefit in clinical trials at a dose of 20 mg orally three times per day for 14 days

    • Treatment was accompanied by reversible thrombocytopenia

  • For ocular microsporidiosis

    • Fumagillin solution (3 mg/mL)

    • Consider concurrent systemic therapy with albendazole

    • Adjunctive management may include corticosteroids to decrease inflammation and keratoplasty

  • Antiretroviral therapy is the best means of controlling microsporidiosis in AIDS patients



  • Optimal means of preventing microsporidial infections are not well understood, but water purification as discussed above and body substance precautions for immunocompromised and hospitalized individuals are likely effective


Almeria  S ...

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