Microsporidiosis

Cause

At least 15 microsporidian species have been recognized as human pathogens, spread across nine genera:

• Anncaliia
  • A. algerae, A. connori, A. vesicularum
• Encephalitozoon
  • E. cuniculi, E. hellem, E. intestinalis
• Enterocytozoon
  • E. bieneusi
• Microsporidium
  • M. ceylonensis, M. africanum
• Nosema
  • N. ocularum
• Pleistophora sp.
• Trachipleistophora
  • T. hominis, T. anthropophthera
• Vittaforma
  • V. corneae.
• Tubulinosema
  • T. acridophagus

The primary causes are Enterocytozoon bieneusi and Encephalitozoon intestinalis.

Life cycle

(Coded to image at right).

1. The infective form of microsporidia is the resistant spore and it can survive for an extended period of time in the environment.
2. The spore extrudes its polar tubule and infects the host cell.
3. The spore injects the infective sporoplasm into the eukaryotic host cell through the polar tubule.
4. Inside the cell, the sporoplasm undergoes extensive multiplication either by merogony (binary fission) or schizogony (multiple fission).
5. This development can occur either in direct contact with the host cell cytoplasm (E. bieneusi) or inside a vacuole called a parasitophorous vacuole (E. intestinalis). Either free in the cytoplasm or inside a parasitophorous vacuole, microsporidia develop by sporogony to mature spores.
6. During sporogony, a thick wall is formed around the spore, which provides resistance to adverse environmental conditions. When the spores increase in number and completely fill the host cell cytoplasm, the cell membrane is disrupted and releases the spores to the surroundings.
7. These free mature spores can infect new cells thus continuing the cycle.

Diagnosis

The best option for diagnosis is using PCR.

Diagnosis with Microsporidia can be done through gram-positive, acid-fast spores in stool and biopsy material with morphologic demonstration of the organism. Initial detection through light microscopic examination of tissue sections, stools, duodenal aspirates, nasal discharges, bronchoalveolar lavage fluids, and conjunctival smears. Definitive diagnosis can also be achieved through fluorescein-tagged antibody immunofluorescence or electron microscopy,

Classification

Although it is classified as a protozoal disease in ICD-10, their phylogenetic placement has been resolved to be within the Fungi, and some sources classify microsporidiosis as a mycosis, however, they are highly divergent and rapidly evolving.

Treatment

Fumagillin has been used in the treatment. Another agent used is albendazole.

Because of its severe mortality risk in immunocompromised individuals, two main agents are used: Albendazole, which inhibits tubulin, and Fumagillin, which inhibits methionine aminopeptidase type two.

References

References

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8. {{MeshName. Microsporidiosis
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14. (November 2018). "Therapeutic targets for the treatment of microsporidiosis in humans". Expert Opin Ther Targets.