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Microsporidiosis
is infection with microsporidia. Symptomatic disease develops predominantly in
patients with AIDS and includes chronic diarrhea, disseminated infection,
and corneal disease. Diagnosis is by demonstrating organisms in
biopsy specimens, stool, urine, other secretions, or corneal scrapings.
Treatment is with albendazole, depending on the infecting species
and clinical syndrome, with topical fumagillin added in eye disease.
Microsporidia are obligate intracellular spore-forming protozoan parasites. At least 14 of the > 1200 species are associated with human disease. Organisms are acquired by ingestion, inhalation, direct contact with the conjunctiva, animal contact, or person-to-person transmission. Inside the host, they uncoil, harpoon a host cell, and inoculate it with an infective sporoplasm. Intracellular division then produces sporoblasts that mature into spores, which can disseminate throughout the body or pass into the environment via respiratory aerosols, stool, or urine. An inflammatory response develops when spores are liberated from host cells.
Little is known about routes of transmission to humans or possible animal reservoirs. Microsporidia probably are a common cause of subclinical or mild self-limited illness in otherwise healthy people, but only a few cases of human infection were reported in the pre-AIDS era.
Microsporidia have emerged as opportunistic pathogens in patients with AIDS. Encephalitozoon bieneusi and E. (formerly Septata) intestinalis can cause chronic diarrhea in patients with AIDS and CD4+ cell counts < 100/μL. Microsporidian species can also infect the biliary tract, cornea, muscles, respiratory tract, genitourinary system, and, occasionally, the CNS.
Symptoms,
Signs, and Diagnosis
Clinical illness caused by microsporidia varies with the parasite species and the immune status of the host. In patients with AIDS, various species cause chronic diarrhea, cholangitis, punctate keratoconjunctivitis, peritonitis, hepatitis, myositis, or sinusitis. Infections of kidneys, gallbladder, and sinuses have occurred. Vittaforma
(Nosema) corneum and several other species can cause ocular infections ranging from punctuate keratopathy with redness and irritation to severe, vision-threatening stromal keratitis.
Infecting organisms can be demonstrated in specimens of affected tissue obtained by biopsy; in stool, urine, CSF, bile, or sputum; or in corneal scrapings. Microsporidia are best seen with special staining techniques and may require electron microscopy. Fluorescence brighteners (fluorochromes) have been used for quick detection of spores in tissues and smears. Immunoassay and PCR-based tests hold promise for the future.
Treatment
Microsporidia infections are usually self-limited in immunocompetent patients, and therapy is seldom necessary. In immunocompromised patients, albendazole (400 mg po bid for 21 days in adults) may be effective in controlling intestinal infection with E. intestinalis. The drug reduces the number of organisms in small-bowel biopsies but does not eliminate infection. Fumagillin 20 mg po tid for 14 days has been used for E. bieneusi, but it has adverse effects. Ocular lesions caused by E. hellem and E. cuniculi have been treated with albendazole 400 mg bid plus fumagillin eyedrops. These drugs are also used for V. corneum, but they frequently fail and keratoplasty may be required. Albendazole 400 mg bid has been used for patients with disseminated disease caused by numerous microsporidian species. There is no established treatment for Pleistophora infections. Treatment of AIDS with highly active antiretroviral therapy is important and can lead to improvement in symptoms.
Last full review/revision November 2005
Content last modified November 2005
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