microsporidiosis

Etiology

• Enterocytozoon bieneusi
• Encephalitozoon cuniculi
• Enterocytozoon hellum
• Septata intestinalis

Epidemiology

• Microsporidia infest a large variety of animals, including humans, but reservoir hosts have not been identified
• serious pathogens in immunocompromised hosts
• may account for 30% of unexplained diarrhea in AIDS patients

Pathology

• organisms multiply intracellularly (merogony)
• spores are formed (sporogony) that rupture the host cell (duodenal enterocyte) & infect adjacent cells or are passed in the feces
• spore contains a coiled polar tubule which is extruded to penetrate the membrane of the recipient cell
• the sporoplasm is injected through the tubule into the cytoplasm of the host cell, where it multiplies

Clinical manifestations

• chronic diarrhea (mean duration 8.5 months)
• weight loss
• dissemination (some species)
• malabsorption
• hepatic, ocular, CNS, muscle manifestation (other species)

Laboratory

• modified trichrome staining of stools for spores
  • 1.5-3 um elliptical spores stain red against a faint green background
  • some spores have band across midsection
• fluorochrome stains of feces
  • Uvitex 2B
  • calcofluor white
  • may be more sensitive than modified trichrome staining
• small size of spores makes detection difficult
• small bowel biopsy
  • trichrome, Brunn & Brenn, or Giemsa stain
  • electron microscopy for species identification
• fecal fat may be positive
• abnormal D-xylose absorption test
• serum albumin is generally normal

Management

• no definitive therapy
• albendazole 400 mg QD for 1 month for intestinal disease
• fumagillin may be effective for keratoconjunctivitis

More general terms

• protozoan infection

Additional terms

• microsporidia