Microsporidia (Phylum Microsporida)

Microsporidia are obligately pathogenic, single-celled, eukaryotic organisms of which nearly 1,000 species have been described, over 700 from insect hosts. Lacking mitochondria, centrioles, peroxisomes and classical Golgi bodies, and possessing a nonmotile amoeba-like vegetative form, microsporidia were considered until recently to be primitive members of the Protozoa. Molecular analyses, however, have determined that the group possesses several gene sequences that suggest a close relationship to the fungi.

The first microsporidium studied was the causal agent of “pebrine disease” of silkworms (Bombyx mori L.), a disease that nearly caused the demise of the silk industry in France in the 1860s. Louis Pasteur recognized the infectious nature of the disease and developed a screening technique to rid the industry silkworm colonies of the pathogen. The microsporidium was later described as Nosema bombycis Naegli, the type species of the well-known genus Nosema.

Microsporidia infect all...