The infective form of microsporidia is the resistant spore, which can persist in the environment for months The spore then germinates, rapidly everting its polar tubule which contacts the eukaryotic host cell membrane. anthropophthera), Nosema ocularum, Pleistophora ronneafiei, Vittaforma corneae (= Nosema corneae), Tubulinosema acridophagus, and an unknown species likely belonging to Endoreticulatus.

Other less frequently reported agents include members of the genera Anncaliia (= Brachiola) ( A. There are at least 15 microsporidian species that have been identified as human pathogens the vast majority of cases being caused by Enterocytozoon bieneusi, followed by some Encephalitozoon species ( E. To date, more than 1400 species belonging to over 200 genera have been described as parasites infecting a wide range of vertebrate and invertebrate hosts. Microsporidia also possess degenerated mitochondria called mitosomes and lack a conventional Golgi apparatus. They possess a unique organelle, the polar tubule or polar filament, which is coiled inside the spore as demonstrated by its ultrastructure. Microsporidia are characterized by the production of resistant spores that vary in size (usually 1-4 µm for medically-important species). The taxonomic position of this group has been debated and revised repeatedly historically, they were considered protozoa and often remain managed by diagnostic parasitology laboratories. The microsporidia are a group of unicellular intracellular parasites closely related to fungi, although the nature of the relation to the kingdom Fungi is not clear.

Frog spore