MSD Manual

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Richard D. Pearson

, MD, University of Virginia School of Medicine

Last full review/revision May 2020| Content last modified May 2020
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Microsporidiosis is infection caused by Microsporidia, which are parasitic fungi. Symptoms depend on the organs infected, but infections can cause diarrhea, other intestinal symptoms, or eye symptoms.

  • Microsporidiosis causes symptoms mainly in people with a weakened immune system, such as people with AIDS.

  • Symptoms vary but include chronic diarrhea, abdominal pain, fever, weight loss, and eye inflammation.

  • Doctors diagnose the infection by identifying microsporidia in a sample of the infected tissue or in stool, urine, or other body fluids.

  • Drugs can control but not eliminate the infection.

Microsporidia used to be classified as protozoa but are now considered fungi. These spore-forming parasitic fungi live inside infected cells.

Microsporidia may infect the intestine, liver, gallbladder, biliary tract (the tubes that connect the liver and gallbladder with the small intestine), eyes, sinuses, muscles, respiratory tract, urinary tract, and, occasionally, the brain. The infection may spread throughout the body.

Several species of Microsporidia can cause infection in people, but symptoms occur mainly in those with advanced AIDS or other disorders that severely weaken the immune system. People with a healthy immune system may develop eye symptoms if microsporidia infect the cornea.

Microsporidia spread through spores, which can

  • Be ingested

  • Be inhaled

  • Enter through tissues around the eye

  • Be spread from person to person

  • Be spread through contact with an infected animal

Inside the body, microsporidia spores enter cells, where the spores develop, multiply, and form more spores. The infected cells eventually rupture, releasing the spores. The spores can then spread throughout the body, causing inflammation, or they can be excreted into the environment in the breath, stool, or urine.


Symptoms of microsporidiosis vary depending on

  • Which species causes the infection

  • Which organs are affected

  • How well a person’s immune system is working

People with a normal immune system typically have no symptoms, but in people with AIDS or other conditions that weaken the immune system, microsporidiosis can cause chronic diarrhea and various infections (such as hepatitis and sinusitis). If microsporidiosis affects the intestine, people may not absorb enough nutrients from food (called malabsorption) leading to weight loss.

Other microsporidiosis symptoms may include abdominal pain, jaundice, fever, persistent cough, muscle aches and pain, headache, and eye inflammation with redness. Vision may be blurred. If infection of the eye is severe, blindness can result.


  • Examination of a sample of affected tissue, stool, urine, or other body fluids

To diagnose microsporidiosis, doctors examine a sample of the affected tissue (taken by biopsy) or a body fluid with a microscope, usually using special techniques to make the microsporidia more visible. For example, samples of stool, urine, blood, sputum, cerebrospinal fluid (taken by spinal tap), or the cornea (taken by scraping) may be examined.

Tests may also be done to identify the parasite's genetic material (DNA) in the sample.


  • Albendazole or fumagillin

  • For people with AIDS, also antiretroviral drugs

  • For eye infection, albendazole (taken by mouth) and fumagillin (as eye drops)

If the immune system is normal, mild cases of microsporidiosis usually resolve without treatment.

In people with AIDS, it is very important that the HIV infection is treated as effectively as possible with antiretroviral drugs. Such treatment can strengthen the weakened immune system, which usually helps control the diarrhea and other symptoms. Likewise, it is important to reverse, if present, other causes of immune suppression.

The antimicrobial treatment of microsporidiosis depends on which microsporidia species is causing the infection, if the person's immune system is normal, and the organ(s) involved. Albendazole, taken by mouth, may help control diarrhea if the species causing the intestinal infection is susceptible to it. However, the drug does not eliminate the infection.

Albendazole is also used to treat microsporidiosis that affects the skin or muscle or that has spread throughout the body if the species causing the infection is susceptible.

Fumagillin tablets taken by mouth have been used to control diarrhea when the infecting microsporidia species is potentially susceptible, but it may have serious side effects. Fumagillin tablets are not available in the United States.

Eye infections are treated with albendazole taken by mouth and fumagillin eye drops. Fluoroquinolone or voriconazole eye drops are sometimes useful. If these drugs do not relieve the symptoms, surgery to repair the cornea (keratoplasty) may be required.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version

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