ABSTRACT
Microsporidia comprise an order of phylogenetically ancient organisms that belong to the subkingdom Protozoa and the phylum Microspora. They are unicellular parasites and are considered to be eukaryotes because they possess a nucleus and nuclear membrane, but resemble prokaryotes in that they lack mitochondria, peroxisomes, and Golgi membranes. The phylum consists of over 100 genera and almost 1000 species. 1 First identified in 1857, 2 these organisms have caused serious economic problems for the silkworm, honeybee, and commercial fishing industries. 3 They are obligate intracellular spore-forming protozoa and are found in many invertebrate and all vertebrate species. Along with members of the phylum Sporozoa including Isos-pora, Cryptosporidia, and Cyclospora, they constitute the four intestinal spore-forming protozoa of humans. 4
