Microsporidiosis

[Lanell]

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) or with topical fumagillin and oral albendazole for eye disease.
(See also Overview of Intestinal Protozoan and Microsporidia Infections.)
Microsporidia are obligate intracellular spore-forming parasites that are fungi or closely related to them. Microsporidia used to be classified as protozoa.
At least 15 of the gt; 1,400 species of microsporidia are associated with human disease. Spores of the organisms are acquired by the following:

Ingestion
Inhalation
Direct contact with the conjunctiva
Animal contact
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—perhaps because overall awareness of microsporidial infection was less. Recently, microsporidial keratoconjunctivitis has become increasingly reported in immunocompetent people.
Microsporidia have emerged as opportunistic pathogens in patients with AIDS and, to a lesser degree, in those with other immunocompromising conditions. Encephalitozoon species including E. bieneusi and E. (formerly Septata) intestinalis can cause chronic diarrhea in patients with AIDS and CD4 cell counts of lt; 100/mcL. Depending on the species and immune status of the host, some Microsporidium, Nosema, Vittaforma, and other genera can infect the eyes, liver, biliary tract, sinuses, muscles, respiratory tract, genitourinary system, central nervous system, and occasionally cause disseminated disease.
The incidence of microsporidiosis in persons with AIDS has decreased substantially with the widespread use of effective antiretroviral therapy.

[Sarah]

Infection with microsporidia.