Microsporidiosis is an important cause of diarrhea in HIV infected patients. Micro-sporidia are obligate intracellular protozoa. At least four genera that are pathogenic in humans have been described. Of these, Enterocytozoon bieneusi is the most important. Microsporidia were previously among the most frequent diarrhea-causing microbes, and in the pre-HAART era, could be found in approximately one third of all patients and in some studies in up to two thirds of all HIV infected patients with chronic diarrhea (Sobottka 1998). The incidence of microsporidiosis has reduced significantly due to HAART, and is now only diagnosed occasionally. Microspo-ridiosis is not AIDS defining, although chronic microsporidiosis almost always occurs in severely immunocompromised patients with CD4-cell counts of less than 50 cells/^l.
Diarrhea may be very severe and is usually watery, though not bloody. It is accompanied by abdominal pain, nausea and vomiting. Fever is almost always absent. Rarely, myositis, keratoconjunctivitis and sinusitis have been described. Infections of the biliary ducts are more frequent.
Even more than in the case of cryptosporidia, it is essential that the laboratory is experienced. Microsporidia are very small, and those who are not explicitly asked to detect them will not find them! Culture has not generally been established. Detection is most successful with specialized staining methods. Special transport or preparation is not necessary.
Albendazole (1-2 tbl. a 400 mg bid for 4 weeks) is quite effective, but certainly not in every case. In particular, E. bieneusi is frequently resistant to albendazole. Positive reports from France of treatment with fumagillin have been published (watch for thrombocytopenia!), but the case numbers remain low (Molina 2002). Case reports (Bicart-See 2000) are also available for niazoxanide (see cryptosporidiosis). Thalidomide can be considered for symptomatic treatment. HAART-induced immune reconstitution, however, seems to have the greatest effect (Carr 1998+2002, Maggi 2000).
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