ИСТИНА

Microsporidia (Phylum Microsporidia Balbiani 1882) are ubiquitous parasites within the Animal Kingdom. The phylum includes 1400 described species belonging to 200 genera. The host range, as well as molecular data, strongly suggest that microsporidia evolved as parasites of invertebrates and, to a lesser extent, fish. Only about 1% of microsporidia species have been found in endothermic vertebrates, birds and mammals. Microsporidiosis in humans has been observed worldwide mainly in patients with HIV infection and now increasingly in other groups such as children, immunosuppressed individuals (e.g. organ transplant recipients), contact lens wearers, travelers, and the elderly. Among AIDS patients, microsporidiosis is listed as the third important opportunistic infection causing gastrointestinal disorders, after Cytomegalovirus and Cryptosporidium. In fact, only four species belonging to two genera can be considered true mammalian parasites: Enterocytozoon bieneusi, Encephalitozoon cuniculi, Enc. intestinalis , and Enc. hellem. These represent a serious threat to human populations as zoonotic infections. Findings of other microsporidia (as a rule, parasites of arthropods or close relatives of those) in humans, are accidental. At the same time these records demonstrate the consecutive stages of microspordida adaptation to parasitism in humans: from transient arthropod-related microsporidia known by sequences in stools of AIDS patients, through accidental surface infections in immunocompromised patients (Endoreticulatus-like Microsporidium sp., Tubulinosema) and development in immune privileged tissues of eyes (Vittaforma), skin, and muscles due to accidental exposure to spores of a “generalist” microsporidium (Trachipleistaphora, Anncaliia), to specialized infections of gut epithelium (Enterocytozoon), and systemic microsporidiosis disseminated by macrophages (Encephalitozoon). The review is addressing the following questions. What is special about the microsporidia that are able to infect warm-blooded? How high are the risks of acquisition of new microsporidia parasites by humans, given abundance of microsporidia in invertebrates, many of which may traverse food chains leading to humans and other mammals?