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United States Department of Agriculture

Agricultural Research Service

Title: Microsporidia: Occurrence, Fate and Methodologies

Author
item Dowd, Scot

Submitted to: Encyclopedia of Environmental Microbiology
Publication Type: Book / Chapter
Publication Acceptance Date: April 1, 2002
Publication Date: April 30, 2002
Citation: Dowd, S.E. 2002. Microsporidia: Occurrence, fate and methodologies. In: Bitton, G., Editor. Encyclopedia of Environmental Microbiology. New York, NY:Wiley and Sons. p. 2077-2083.

Interpretive Summary: Microsporidia is a non-taxonomic term used to describe a group of protozoa, which belong to the phylum Microspora. Microsporidia may be the most ancient branch of the eukaryotic tree. Though microsporidia have a nucleus, they lack mitochondria, peroxisomes, and their ribosomal characteristics are more closely related to bacteria than to higher eukaryotes. In addition, the human enteropathogenic microsporidia (HEM) are closer in size to bacteria (~1-2µm diameter) than to most other protozoan parasites such as Giardia lamblia (~15µm diameter) and Cryptosporidium parvum (~5µm diameter). Microsporidia have an environmentally resilient spore wall that consists of a proteinaceous exospore and a chitinous endospore. The HEM cause chronic diarrhea and wasting in HIV infected individuals. Estimates indicate that from 7 to 50% of those immunodeficient patients are infected with HEM making it one of the most important intestinal pathogens in these populations. No reports on the infective dose of the HEM have been documented but indications are that it is very low especially in the immunocompromised. In immunocompetent individuals a similar form of diarrhea, to that seen in the immunocompromised, is evident but is self-limiting. Asymptomatic infections have also been reported in both HIV infected and immunocompetent patients. Finally, as improved methods for clinical detection of HEM are developed increasing reports of infection in the immunocompetent are being described indicating that the HEM may also be an important pathogen in individuals not infected with HIV. This article reviews the basics of microsporidia and describes current methods for their detection in the environment.

Technical Abstract: Microsporidia is a term used to describe a group of small microorganisms that can infect many different organisms including humans. Microsporidia may be the most ancient of cellular organisms with a nucleus. Microsporidia are similar in size to bacteria (~1-2µm diameter). Microsporidia have an environmentally resilient spore wall that consists of a protein and chitin. Some microsporidia infect humans and cause chronic diarrhea and wasting in infected individuals with compromised immune systems. Estimates indicate that from 7 to 50% of those immunodeficient patients are infected with microsporidia making it one of the most important intestinal pathogens in these populations. Improved methods are needed for clinical and environmental detection of these newly emerging pathogens. This article reviews the basics of microsporidia and describes current methods for their detection in the environment.

Last Modified: 10/1/2014
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