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 or fumagillin (depending on the infecting species and clinical syndrome), with topical fumagillin added for eye disease.
Microsporidia are obligate intracellular spore-forming protozoan parasites. At least 14 of the > 1200 species are associated with human disease. Spores of the organisms are acquired by ingestion, inhalation, direct contact with the conjunctiva, animal contact, or person-to-person transmission. Inside the host, they harpoon a host cell with their polar tubule or filament and inoculate it with an infective sporoplasm. Intracellularly, the sporoplasm divides and multiplies, producing sporoblasts that mature into spores; the spores 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 and, to a lesser degree, in those with other immunocompromising conditions. Encephalitozoon bieneusi and E. (formerly Septata) intestinalis can cause chronic diarrhea in patients with AIDS and CD4+ cell counts of < 100/μL. Microsporidian species can also infect the biliary tract, cornea, muscles, respiratory tract, GU system, and, occasionally, the CNS.
Symptoms and Signs
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, malabsorption, wasting, 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 or in stool, urine, CSF, sputum, or corneal scrapings. Microsporidia are best seen with special staining techniques. Fluorescence brighteners (fluorochromes) are used to detect spores in tissues and smears. The quick-hot Gram chromotrope technique is the fastest. Immunoassay and PCR-based tests hold promise for the future.
Transmission electron microscopy is currently the most sensitive test and is used for speciation.
In immunocompetent patients, microsporidia infections are usually self-limited, 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 (eg, bone marrow suppression).
Ocular lesions (due to Brachiola algerae, E. hellem, or 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 and skin and deep muscle infection caused by numerous microsporidian species.
Treatment of AIDS with highly active antiretroviral therapy (HAART) is important and can lead to reduction in symptoms.
Last full review/revision December 2009 by Richard D. Pearson, MD