Microsporidiosis - Microsporidia - HIV/AIDS Definition

Microsporum.JPG used under a Creative Commons license at http://en.wikipedia.org/wiki/Microsporum#mediaviewer/File:Macroconidia_Microsporum_canis.JPG
Microsporum canis. Photograph © Roberto J. Galindo

Definition: Microsporidiosis is an opportunistic disease caused by different species of the unicellular fungi, microsporidia. The disease, which can affect the gastrointestinal tract and other parts of the body, is almost always seen in individuals with severely compromised immune systems, such as those with HIV. More often than not, infection occurs when the person's CD4 count drops below 100 cells/mL.

While microsporidiosis is most frequently associated with a range of gastrointestinal symptoms, including severe diarrhea and wasting, certain types of microsporidia can affect the kidneys, lungs, sinuses, eyes and central nervous system, as well.

Initially thought to be a protozoan pathogen, genetic research later confirmed microsporidia to be a member of the fungi kingdom. There are currently 14 microsporidia species known to infect humans.

Prevalence Rates

The current evidence seems to suggest that the prevalence of microsporidiosis among HIV-infected Americans is low, roughly 1.6%. However, other studies have shown that the prevalence of microsporidial infection in those later-stage individuals with chronic or severe diarrheal symptoms is high, more around 39%.

Modes of Transmission

Transmission of microsporidia is still not entirely clear, although research seems to suggest that the fungal spores may be ingested, inhaled, or even passed through vulnerable mucosal tissues (such as the eye).

During infection, the spores multiply within the cytoplasm (i.e., the interior fluid) of infected cells, with some species—like Encephalitozooan intestinalis—affecting severe diarrhea, while others—like Encephalitozoon cuniculi—impacting the kidneys and central nervous system.

Symptoms of Microsporidiosis

While immune competent individuals may be diagnosed with microsporidiosis, by and large, the disease is seen in those with AIDS.

When impacting the gastrointestinal tract, severe diarrhea and wasting are often noted, oftentimes in the absence of fever, inflammation or high fever. Oftentimes, the symptoms are indistinguishable from that of cystoisosporiasis and cryptosporidiosis.

Symptoms can be far-ranging (depending on which species of microsporidia one is infected with) and may include:

  • Cough, wheezing and labored breathing
  • Atypical urinary tract infection
  • Muscular weakness and pain
  • Headaches and migraines
  • Blurred vision, light sensitivity, eye pain, excessive tearing
  • Nasal congestion, sinus pain
  • Inflamed gallbladder

Diagnosis of Microsporidiosis

Diagnosis of microsporidiosis is supported by the presentation of clinical features and symptomatology; pre-test probability (a subjective assessment of the likelihood of infection in an individual); and the analyses of feces, urine, body tissue, or other bodily fluids.

Transmission electron microscopy, although expensive, can provide a definitive diagnosis by clearly identifying the microsporidia spores.

Alternately, gram stained light microscope are considered effective in identifying spore infiltration.

Genetic PCR (polymerase chain reaction) tests are available for microsporidia identification, but almost entirely in research settings only.

Treatment of Microsporidiosis

As microsporidiosis is generally associated with severe immune suppression, it is advised that combination antiretroviral therapy (cART) be administered as part of the initial course of action.

The azole drug, albendazole, can be used be used in the treatment of microsporidia, particularly with species like E. intestinalis, although some studies have shown it to be less effective in treating other species. Itraconazole is also frequently used with albendazole in disseminated disease (i.e., when it has spread beyond the original site of presentation).

The antifungal fumagillin is also considered a viable option, with some studies suggesting that it has superior action in cases of E. bienusi infections.  However, it is not available for systemic use in the United States. Topical fumagillin drops are available for infections of the eye, although it is recommended for use in conjunction with albendazole therapy.

Please note, however, that it the use of albendazole is currently not recommended during the first trimester of pregnancy due to animal tests that suggest a risk of fetal birth defects. There is currently insufficient data as to the use of albendazole in human pregnancy.

Prevention of Microsporidiosis

As the etiology (cause) of microsporidiosis is not entirely clear, it is advised that immune-compromised individuals follow the same guidelines for cystoisosporiasis, which includes avoiding untreated water, raw meat, or raw seafood.

Pronunciation: mi-kro-spo-rid-ee-OH-suhs

Sources:

Keeling, P.; and  Madhani, H. "Five Questions about Microsporidia". PLoS|Pathogens. September 2009; 5(9): e1000489.

U.S. Department of Health and Human Services (DHHS). "Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescent – Microsporidiosis." Rockville, Maryland; updated May 7, 2013

Dworkins, M.; Buskin, S.; Davidson, A.; et al. "Prevalence of intestinal microsporidiosis in human immunodeficiency virus-infected patients with diarrhea in major United States cities." Revista do Instituto de Medicina Tropical de São Paulo. November-December 2007; 49(6):339-342.

Kotler, D. and Orenstein, J. "Prevalence of intestinal microsporidiosis in HIV-infected individuals referred for gastroenterological evaluation."  American Journal of Gastroenterology. November 1994; 89(11):1998-2002.

Molina, J.; Tourneur, M.;  Sarfati, C.; et al. "Fumagillin treatment of intestinal microsporidiosis". New England Journal of Medicine. June 2002: 346(25): 196319699.

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