eMedicine Specialties > Infectious Diseases > Parasitic Infections

Microsporidiosis

Author: Valda M Chijide, MD, Clinical Professor, Department of Medicine, University of Saskatchewan; Consultant in Infectious Diseases, Regina, Saskatchewan, Canada
Contributor Information and Disclosures

Updated: Sep 18, 2009

Introduction

Background

Microsporidiosis (also known as microsporidiasis) is caused by infection with microsporidia, which are obligately intracellular, spore-forming parasites that belong to the phylum Microspora and the order Microsporida. Microsporidia are eukaryotic organisms that contain 70S ribosomes but lack mitochondria, peroxisomes, Golgi membranes, and other typically eukaryotic organelles. The phylum Microspora contains over 1000 species. They are ubiquitous organisms with an extensive host range, including honeybees, fish, mosquitoes, ticks, grasshoppers, rodents, rabbits, and other fur-bearing mammals. Species identified as causing microsporidiosis in humans include the following:

  • Enterocytozoon bieneusi
  • Encephalitozoon hellem
  • Encephalitozoon intestinalis (previously Septata intestinalis)
  • Encephalitozoon cuniculi
  • Pleistophora species
  • Trachipleistophora hominis
  • Trachipleistophora anthropophthera
  • Nosema connori (as seen in the image below)

  • Electron micrograph (X30,000) of <em>Nosema conno...

    Electron micrograph (X30,000) of Nosema connori in diaphragm showing a coiled polar filament (arrow). Courtesy of the Armed Forces Institute of Pathology (AFIP 71-11521-4).

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    Electron micrograph (X30,000) of <em>Nosema conno...

    Electron micrograph (X30,000) of Nosema connori in diaphragm showing a coiled polar filament (arrow). Courtesy of the Armed Forces Institute of Pathology (AFIP 71-11521-4).

  • Nosema ocularum
  • Brachiola vesicularum
  • Vittaforma corneae (previously Nosema corneum)
  • Microsporidium ceylonensis
  • Microsporidium africanum
  • Brachiola algerae

Currently, most cases of human microsporidiosis are associated with HIV infection or other forms of immunosuppression, particularly in organ transplant recipients; however, cases have been reported in immunocompetent individuals.

Pathophysiology

Humans acquire microsporidiosis through ingestion or inhalation of microsporidia spores. Studies have isolated Encephalitozoon species in the urinary tract in those with disseminated infections, suggesting that sexual transmission is possible. The spore is the infective form. Spores are environmentally resistant and are surrounded by an outer electron-dense glycoprotein layer and an electron-lucent endospore layer composed primarily of chitin. The spore extrudes its polar tubule and injects the infective sporoplasm into the host cell. Once inside the cell, it multiplies by binary fission or schizogony. Development can occur directly inside the host cell cytoplasm or inside parasitophorous vacuoles. As mature spores develop and accumulate, the cell expands and eventually ruptures, releasing the spores.

Frequency

United States

Currently, most cases of microsporidiosis are reported in immunosuppressed adults, especially those with HIV-related immunosuppression. Studies have found that E bieneusi infection of small intestinal enterocytes is detected in 15-34% of patients with AIDS with chronic diarrhea and no other identified causes.

E bieneusi infection has also been found in renal transplant recipients with chronic weight loss and diarrhea. A case of fatal myositis due to B algerae infection has been documented in a woman with diabetes and rheumatoid arthritis who had been prescribed infliximab.1

International

Microsporidia have a worldwide distribution. Cases of microsporidiosis have been reported in both developed and developing countries and among both immunosuppressed and immunocompetent individuals. Microsporidiosis has been reported in the Americas, Asia, Europe, and Africa.

Mortality/Morbidity

Clinical symptoms and manifestations of microsporidiosis depend on the infecting species and the host's immune status. Microsporidial keratoconjunctivitis has been identified in healthy immunocompetent individuals, and the use of topical steroids may have been the initial predisposing factor in one case series.2 The individuals in this case series exhibited unilateral punctate epithelial involvement of the cornea. V corneae infection was identified as a cause of unilateral stromal keratitis in a case report by Font et al, and topical steroid use had also preceded the diagnosis.3

  • Bilateral punctate epithelial involvement of the cornea is the typical manifestation of ocular microsporidiosis in immunocompromised individuals.
  • Most cases of intestinal and disseminated microsporidiosis in patients infected with HIV are reported in those who are severely immunocompromised (CD4 <100/µL); in these patients, morbidity can be significant. E bieneusi infections often result in protracted debilitating illness with diarrhea, which may last several months. E bieneusi infections carry a mortality of up to 56%. In addition to chronic diarrhea, malabsorption and wasting can occur in persons with AIDS. E bieneusi is responsible for more than 90% of intestinal microsporidiosis cases in this population; E intestinalis accounts for the remainder.
  • Reports of E bieneusi infections are increasing among travelers and residents of tropical countries who do not have HIV infection. E intestinalis infection associated with chronic diarrhea has been reported in immunocompetent travelers.
  • E bieneusi is usually found only in enterocytes. E intestinalis is more invasive and produces disseminated disease involving the small and large intestines, gallbladder, urinary tract epithelium, and respiratory tract epithelium. Biliary tract involvement that progresses to cholangitis and cholecystitis is common in patients with AIDS who have E bieneusi infection.
  • Myositis due to Pleistophora infection has been documented.

Race

Microsporidiosis has no known racial predilection.

Sex

Microsporidiosis has no known gender predilection.

Age

Microsporidiosis has no known age predilection.

Clinical

History

  • Intestinal or biliary microsporidiosis
    • Chronic diarrhea (loose, watery, nonbloody)
    • Weight loss
    • Abdominal pain
    • Nausea
    • Vomiting
  • Disseminated microsporidiosis
    • Symptoms of cholecystitis, renal failure, and respiratory tract infections occur.
    • Patients with respiratory tract involvement may present with persistent cough, dyspnea, and wheezing.
    • Headache, nasal congestion or discharge, ocular pain, and loss of taste may indicate sinus involvement.
    • Patients with urinary tract involvement are frequently asymptomatic.
  • Ocular microsporidiosis
    • Foreign body sensation, eye pain, or both
    • Light sensitivity
    • Ocular redness
    • Excessive tearing
    • Blurred or decreased vision
  • Musculoskeletal microsporidiosis: Myalgia, generalized muscle weakness, and fever are common in patients with myositis and severe cellular immunodeficiency.
  • Dermatologic microsporidiosis: Microsporidia have been associated with a nodular cutaneous lesion in patients with HIV infection.
  • CNS microsporidiosis: Patients with microsporidiosis of the brain may experience seizures and headache.

Physical

  • Head, eyes, ears, nose, and throat (HEENT) examination
    • Patients with ocular involvement due to Encephalitozoon infection may develop conjunctival hyperemia. A slit-lamp examination may reveal keratoconjunctivitis, which is characterized by diffuse, superficial, punctate keratopathy. The infection is frequently bilateral in immunosuppressed individuals.
    • Corneal ulceration is rare in patients with AIDS who have microsporidiosis. Retinal involvement has not been reported.
    • Those in whom microsporidiosis involves the sinuses may have nasal crusting or purulence, polypoid tissue, or thickened and granular-appearing mucosa.
  • Abdominal examination
    • Patients with intestinal or biliary microsporidiosis may have abdominal tenderness.
    • Clinical jaundice due to microsporidiosis is rare.
    • Severe wasting and signs of malnourishment are usually observed in patients with prolonged severe diarrhea.
  • Musculoskeletal examination: Muscle tenderness and generalized weakness may be noted in patients with microsporidiosis-related myositis.
  • Skin examination: A skin examination may reveal nodules or necrotic lesions.

Causes

  • Microsporidiosis is believed to be a zoonosis. Evidence suggests that microsporidia may be water-borne pathogens and may be transmitted from human to human.
  • Most cases of microsporidiosis in patients with HIV infection occur in those with severe immunodeficiency.
  • Cases of microsporidiosis have been reported in individuals who are HIV negative and who are immunocompromised secondary to transplant surgery or prolonged steroid use.
  • Self-limited diarrhea due to microsporidiosis has been reported in immunocompetent travelers; waterborne transmission may play a role in these cases.

More on Microsporidiosis

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

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Keywords

microsporidiosis, microsporidiasis, microsporidia, Enterocytozoon bieneusi, E bieneusi, Encephalitozoon hellem, E hellem, Encephalitozoon intestinalis, E intestinalis, Septata intestinalis, S intestinalis, Encephalitozoon cuniculi, E cuniculi, Pleistophora, Trachipleistophora hominis, T hominis, Trachipleistophora anthropophthera, T anthropophthera, Nosema connori, N connori, Nosema ocularum, N ocularum, Brachiola vesicularum, B vesicularum, Vittaforma corneae, V corneae, Nosema corneum, N corneum, Microsporidium ceylonensis, M ceylonensis, Microsporidium africanum, M africanum, microsporidial keratoconjunctivitis, ocular microsporidiosis, intestinal microsporidiosis, disseminated microsporidiosis, biliary microsporidiosis

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Contributor Information and Disclosures

Author

Valda M Chijide, MD, Clinical Professor, Department of Medicine, University of Saskatchewan; Consultant in Infectious Diseases, Regina, Saskatchewan, Canada
Valda M Chijide, MD is a member of the following medical societies: American College of Physicians, HIV Medicine Association of America, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Medical Editor

Joseph Richard Masci, MD, Chief of Infectious Diseases, Associate Director, Associate Professor, Department of Internal Medicine, Division of Infectious Diseases, Elmhurst Hospital Center, Mount Sinai School of Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

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, 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

Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

 
 
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