Microsporidiosis

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Overview

Microsporidiosis
ICD-10	B60.8
ICD-9	136.8
DiseasesDB	31870
MeSH	D016881

Microspridiosis is an opportunistic intestinal infection that causes diarrhea and wasting in immunocompromised individuals (HIV, for example). It results from different species of microsporidia, a group of protozoal parasites.

In HIV infected individuals, microsporidiosis generally occurs when CD4+ T cell counts fall below 100.

Causative agents

At least 14 microsporidian species have been recognized as human pathogens, spread across eight genera:

• Brachiola
  • B. algerae, B. connori, B. 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.

Life cycle

Life cycle of the various organisms that cause microsporidiosis.

(Coded to image at right).

1. The infective form of microsporidia is the resistant spore and it can survive for an exteneded 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.

Treatment Recommendations

ART with immune restoration (an increase of CD4+ T lymphocyte count to >100 cells/µL) is associated with resolution of symptoms of enteric microsporidiosis, including that caused by E. bieneusi. All patients should be offered ART as part of the initial management of their infection (AII). Nevertheless, data indicate that microsporidia are suppressed but not eliminated.

Management of Treatment Failure

Supportive treatment and optimizing ART to attempt to achieve full virologic suppression are the only feasible approaches to the management of treatment failure (CIII).

Prevention of Recurrence

Treatment for ocular microsporidiosis should be continued indefinitely because recurrence or relapse might follow treatment discontinuation (BIII). Whether treatment can be safely discontinued after immune restoration with ART is unknown, although it is reasonable, on the basis of the experience with discontinuation of secondary prophylaxis (chronic maintenance therapy) for other opportunistic infections during advanced HIV-1 disease, to discontinue chronic maintenance therapy if patients remain asymptomatic with regard to signs and symptoms of microsporidiosis and have a sustained (e.g. >6 months) increase in their CD4+ T lymphocyte counts to levels >200 cells/µL after ART (CIII).

Special Considerations During Pregnancy

Among animals (i.e., rats and rabbits), albendazole is embryotoxic and teratogenic at dosages of 30 mg/kg body weight. Therefore, albendazole is not recommended for use among pregnant women (DIII). However, well-controlled studies in human pregnancy have not been performed. Systemic fumagillin has been associated with increased resorption and growth retardation in rats. No data on use in human pregnancy are available. However, because of the antiangiogenic effect of fumagillin, this drug should not be used among pregnant women (EIII). Topical fumagillin has not been associated with embryotoxic or teratogenic effects among pregnant women and might be considered when therapy with this agent is appropriate (CIII).

External links

• CDC's microsporidiosis info page.

Reference

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