Microsporidia
| Microsporidia | |
|---|---|
| Sporoblast of Fibrillanosema crangonycis | |
| Scientific classification | |
| Domain: | Eukaryota |
| Clade: | Obazoa |
| Clade: | Opisthokonta |
| Clade: | Holomycota |
| Kingdom: | Fungi |
| Subkingdom: | Rozellomyceta |
| Phylum: | Rozellomycota |
| Class: | Microsporidia ex Corliss & Levine 1963 |
| Orders | |
(A number of former classes and orders are moved to Rozellomycota.) | |
| Synonyms | |
| |
Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or protists, but are now known to be fungi, or a sister group to true fungi. These fungal microbes are obligate eukaryotic parasites that use a unique mechanism to infect host cells. They have recently been discovered in a 2017 Cornell study to infect Coleoptera (beetles) on a large scale. So far, about 1500 of the probably more than one million species are named. Microsporidia are restricted to animal hosts, and all major groups of animals host microsporidia. Most infect insects, but they are also responsible for common diseases of crustaceans and fish. The named species of microsporidia usually infect one host species or a group of closely related taxa. Approximately 10 percent of the known species are parasites of vertebrates—several species, most of which are opportunistic, can infect humans, in whom they can cause microsporidiosis.
After infection they influence their hosts in various ways and all organs and tissues are invaded, though generally by different species of specialised microsporidia. Some species are lethal, and a few are used in biological control of insect pests. Parasitic castration, gigantism, or change of host sex are all potential effects of microsporidian parasitism (in insects). In the most advanced cases of parasitism the microsporidium rules the host cell completely and controls its metabolism and reproduction, forming a xenoma.
Replication takes place within the host's cells, which are infected by means of unicellular spores. These vary from 1–40 μm, making them some of the smallest eukaryotes. Microsporidia that infect mammals are 1.0–4.0 μm. They also have the smallest eukaryotic genomes.
The terms "microsporidium" (pl. "microsporidia") and "microsporidian" are used as vernacular names for members of the group. The name Microsporidium Balbiani, 1884 is also used as a catchall genus for incertae sedis members.