Microsporidia

The microsporidia (Microsporidia or also Microsporidiomycetes) are a group of fungi that are intracellular parasites of animals and some protozoa. About 800 species have been described.

They were classified as protozoa, as protists, and as fungi. In reality, they are a basal group of obligate parasitic fungi that descend from unicellular organisms similar to rosellas, which, in the evolutionary process of their adaptation to parasitic life, have lost their mitochondria.

Recent phylogenetic studies propose to classify Rozellomycetes together with Microsporidia in a Rozellomycota division, since according to studies Rozellomycetes could be a paraphyletic group of microsporidia. Several molecular analyzes confirm that Microsporidia and Rozellomycetes comprise sister groups, while the other group Aphelidiomycota had been placed with them in the taxon Opisthosporidia, but recent studies have found it to be more closely related to Eumycota.

Features

Microsporidia, as their name indicates, are characterized by their minimum-sized spores, from 2 to 20 µm, which contain the sporoplasm (the infective parasite) and a simple polar filament. One of the spore walls contains chitin, another fungal trait. They have chitinous cell walls like fungi, although this can be lost during absorption due to parasitism.

Mature parasites, trophozoids, sometimes produce zygotes by meiosis, which can subsequently produce more spores. Reproduction can be sexual or asexual. They present opisthocontous uniflagellate zoospores that have a solid rhizoplast associated with a long kinetosome. They penetrate the host cells through a germ tube and absorb the internal contents of the host organelles, obtaining nutrients through them.

Phylogenetic relationships

Hamiltosporidium magnivora.

Microsporidia are obligate intracellular parasites of various animal species, infecting both vertebrates and invertebrates and some protozoa. The term microsporidium is a common designation, used to name a group of microorganisms characterized by the production of small spores and the lack of mitochondria.

The absence of plastids or mitochondria suggested that they were very primitive forms, separate descendants of the first eukaryotes, which were called archezoa, prior to the symbiosis that gave rise to those organelles. It was striking that the ribosomes of the microsporidium Vairimorpha necathrix showed dimensions typical of those of bacteria, not eukaryotes. Phylogenetic analysis of ribosomal and other genes has shown that the group consists of several independent derivations, reduced by parasitism, of basal forms of the kingdom Fungi. Further examination of ribosomal RNA confirmed that this was a typical reduction in parasitism.

Microsporidiosis can cause a variety of diseases in humans involving multiple organs including: intestine, eye, lung, sinus, kidney, and muscle; both in immunocompromised and immunocompetent. After the gastrointestinal system, ocular microsporidiosis is the most frequent manifestation in humans. The two ophthalmological clinical entities of microsporidiosis are: deep corneal stromal infection in immunocompetent patients and superficial keratoconjunctivitis in patients with AIDS2 and more recently also found in immunocompetent patients Ocular manifestations include superficial punctate keratoconjunctivitis and stromal keratitis, which will depend on the immunological status of patient.

Keratoconjunctivitis is usually found in immunocompromised patients or in contact lens wearers; mainly by the Encephalitozoon gene, while stromal keratitis is caused by Nosema and Microsporidium. However, recent reports have suggested that keratoconjunctivitis can also occur in immunocompetent patients. Davis et al, reported a case of stromal keratitis caused by microsporidiosis in a healthy patient, with no history of trauma. Pinnolis et al and Ashton et al described two cases of corneal involvement in an 11-year-old boy from Sri Lanka with a corneal ulcer, and a 26-year-old woman from Botswana with a perforated corneal ulcer, both patients without significant history and negative serology for HIV.

Natural history

Microsporidia parasitize the intestinal cells of mammals, fish and birds, although they have also been found in invertebrates (Nosema causes pebrin, a disease of Bombyx mori silkworms i>, as described by Louis Pasteur). Apart from animals, microsporidia also parasitize some protozoa such as ciliates.

Nosema apis is a microsporidium that causes a disease called nosemosis, which attacks honey bees, causing intestinal inflammation and diarrhea. The antibiotic used in the treatment of this disease is fumagillin.

Taxonomy

The proposed taxonomy for microsporidia is roughly as follows. Although microsporidia are considered fungi, they should continue to use the Zoological Nomenclature Code traditionally used in protists due to the great taxonomic heritage through which they have passed.

• Subclass: Dihaplophasea.
  • Order: Meiodihaplophasida.
    • Superfamily Thelohanioidea.
      • Thelohaniidae family.
      • Duboscqiidae family.
      • Janacekiidae family.
      • Pereziidae family.
      • Striatosporidae family.
      • Cylindrosporidae family.
    • Superfamily Burenelloidea.
      • Burenellidae family.
    • Superfamily Amblyosporoidae.
      • Amblyosporidae family.
  • Order Dissociodihaplophasida.
    • Nosematoid superfamily.
      • Nosematidae family.
      • Ichthyosporidiidae family.
      • Caudosporidae family.
      • Pseudopleistophoridae family.
      • Mrazekiidae family.
    • Superfamily Culicosporoidea.
      • Culicosporidae family.
      • Culicosporellidae family.
      • Golbergiidae family.
      • Spragueidae family.
    • Superfamily Ovavesiculoidea.
      • Ovavesiculidae family.
      • Tetramicridae family.
• Subclase Haplophasea.
  • Glugeida order.
    • • Glugeidae family.
      • Pleistophoridae family.
      • Encephalitozoonidae family.
      • Abelsporidae family.
      • Tuzetiidae family.
      • Microfilidae family.
      • Unikaryonidae family.
  • Order Chyridiopsida.
    • • Chyridiopsidae family.
      • Buxtehudiidae family.
      • Enterocytozoonidae family.
      • Burkeidae family.
• Subclass Metchnikovellea
  • Order Metchnikovelli
    • Family Amphiacanthidae
    • Metchnikovellidae