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Microsporidiosis

Last updated Nov. 24, 2018

Microsporidiosis is infection by a group of intracellular fungi collectively known as Microsporidia. The transmission of infection to humans take place through contaminated water.


What are the other Names for this Condition? (Also known as/Synonyms)

  • Microspora Infection
  • Microsporan Infection
  • Microsporidea Infection

What is Microsporidiosis? (Definition/Background Information)

  • Microsporidiosis is infection by a group of intracellular fungi collectively known as Microsporidia. The transmission of infection to humans take place through contaminated water
  • Microsporidia are a very large family of parasitic fungi characterized by their production of spores. The spores are the single-celled, reproducing form of fungi that are highly-resistant to destruction. There are over 1,200 species included under this classification
  • There are 15 species of Microsporidia that are known to have infected humans. Each of these species are known to infect specific tissue types, and thus, present with a wide variety of species-specific symptoms
  • However, diarrhea and abdominal pain are reported to be common to most infections. A healthcare provider typically diagnoses Microsporidiosis upon examination of a stool sample
  • Treatment measures may include a combination of anti-parasitic and antimicrobial drugs to offer relief to the affected individual. Once infected, the individuals often require lifelong treatment of symptoms
  • However, the prognosis of Microsporidiosis is generally good with adequate treatment. Preventive methods are not clearly specified for Microsporidiosis

Who gets Microsporidiosis? (Age and Sex Distribution)

  • Individuals of all ages, races, ethnic groups, and genders are susceptible to contracting various forms of Microsporidiosis
  • Microsporidiosis is reported in one form or another, such as gastrointestinal, ocular, respiratory and genitourinary Microsporidiosis, in all regions of the world

What are the Risk Factors for Microsporidiosis? (Predisposing Factors)

Although any individual can develop Microsporidiosis, the risk for contracting infection is highest in individuals having compromised immunity, which may occur owing to conditions such as:

  • HIV infection and AIDS
  • Being on drugs for immune suppression (such as during an organ transplantation)
  • Chemotherapy and/or radiation therapy for cancer treatment

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Microsporidiosis? (Etiology)

Microsporidiosis is caused by the infection and rapid spread of the spore form of Microsporidia, a fungal parasite, in a human host.

  • Microsporidia spread in the form of a resistant spore (a single-cell organism capable of surviving for extended periods of time in harsh environments before getting to a stage of reproduction)
  • These parasites have a characteristic polar tubule (much like an extendable arm) that they can project from themselves and use to penetrate the cells of the humans they have infected. The fungi use this arm to spread and reproduce inside of the cells of their host
  • These fungi are known to primarily infect insects, but contact with spore-contaminated water by humans can allow the spread of Microsporidia to human hosts
  • 15 species of Microsporidia are known to have human hosts. Infection of different parts of the body take place, based on the particular species. Among the 15, the 6 most common species infect the following areas of their human host:
    • Anncaliia algerae - skin or deep muscle infection
    • Anncaliia connori - ocular (relating to the eye) infection
    • Encephalitozoon cuniculi - respiratory and genitourinary infections
    • Encephalitozoon heliem - respiratory and genitourinary infections
    • Encephalitozoon intestinalis - GI or digestive tract infection that can spread to ocular, genitourinary, and respiratory systems
    • Vittaforma corneae - ocular or urinary tract infection

What are the Signs and Symptoms of Microsporidiosis?

Due to the wide range of Microsporidia species that can potentially cause Microsporidiosis, the symptoms of this infection can vary in type and severity among affected individuals. Diarrhea is common to most types of infection.

Symptoms specific to the 6 common microsporidial infections include:

  • Anncaliia algerae
    • Infection of the skin
    • Eye infection, causing keratoconjunctivitis (inflammation of the cornea of the eye), causing foreign body sensations, eye pain, light-sensitivity, redness, excessive tearing, or blurred vision
    • Myositis (mild to extreme inflammation of the muscle tissue)
  • Anncaliia connori
    • Cardiovascular infections can cause heart failure
    • Renal system infections can cause kidney failure or other urinary imbalances
    • Endocrine system infections can cause hormonal imbalance
    • Disseminated or widespread infections (involving the bloodstream) can cause a variety of blood-related conditions
  • Encephalitozoon cuniculi 
    • Cerebral infections causing seizures and neurological dysfunction
    • Disseminated or widespread infections (involving the bloodstream) can cause a variety of blood-related conditions
  • Encephalitozoon hellem
    • Infection of the eye, sinus, and nasal tissue can cause keratoconjunctivitis, which can result in foreign body sensations, eye pain, light-sensitivity, redness, excessive tearing, or blurred vision
    • Respiratory infections can cause difficulty breathing
    • Disseminated or widespread infections (involving the bloodstream) can cause a variety of blood-related conditions
  • Encephalitozoon intestinalis
    • Infection of the epithelium of the intestine can cause diarrhea, malabsorption, and wasting (including weight loss)
    • Infection of the liver, which can cause jaundice 
    • Infection of the renal system
    • Infection of the colon, gallbladder
    • Infection of the lungs
    • Infection of the conjunctiva (a membrane covering the eye/eyelid infections) and sinuses, which can cause keratoconjunctivitis, which results in foreign body sensations, eye pain, light-sensitivity, redness, excessive tearing, or blurred vision
  • Vittaforma corneae
    • Infection of the eye and that results in keratoconjunctivitis, causing foreign body sensations, eye pain, light-sensitivity, redness, excessive tearing, or blurred vision

How is Microsporidiosis Diagnosed?

The diagnosis of Microsporidiosis is made with information from the following:

  • A complete physical examination and an assessment of symptoms
  • An evaluation of medical history
  • Examination of fecal matter of the infected individual through light microscopy. This is usually done with a chemical stain that differentiates nuclear and cytoplasmic material

Although identification of the parasite may be sufficient for treatment purposes in most cases, further analysis may be necessary for the determination of the specific microsporidial species present in the infected individual. These may include:

  • Transmission electron microscopy (TEM): A microscopy technique with resolution up to 10000x that of a light microscope. Characterization of the specific species of microsporidia is based most heavily on the number, location, and arrangement of polar tubule arms. However, TEM is expensive and time-consuming, and therefore often not used, unless deemed necessary
  • Polymerase chain reaction (PCR), in which a species-specific DNA sample is amplified for study can be used for the identification of Microsporidia species that is involved
  • Immunofluorescence, which uses fluorescent antibodies to bind proteins characteristic to specific species of Microsporidial infections

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional test to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Microsporidiosis?

The potential complications of Microsporidiosis may include:

  • Irreparable damage done to infected organ systems owing to delayed or lack of treatment
  • Blindness
  • The following organs may be affected:
    • Kidney
    • Liver
    • Brain

Severe organ failure along-with the associated complications may be fatal.

How is Microsporidiosis Treated?

Treatment of Microsporidiosis is often complicated and a complete eradication of Microsporidia through drug treatment is rarely achieved. Due to the wide range of infections and symptoms related to Microsporidiosis, prescription medication normally targets specific types of infection and is paired with medication used to treat symptoms of Microsporidiosis.

The following drug types are commonly used:

  • Anthelmintic drug for oral ingestion. Although anthelmintic are used to kill parasitic worms, these may be used for Microsporidiosis to provide relief from symptoms such as persistent diarrhea. Examples of anthelmintic drug include Albendazole
  • Oral medication of Fumagillin, an antimicrobial drug, may be prescribed for gastrointestinal symptoms
  • For ocular symptoms, eye drops containing Albendazole and/or Fumagillin bicylohexylammonium may be prescribed for relief from symptoms
  • If the eye drops are not successful, surgery may be required to repair the affected cornea
  • Antiretroviral treatment is the primary treatment for those with suppressed/compromised immunity who are infected with Microsporidia. This can help them reconstitute their immune systems and enable them to fight the infection better
  • Some affected individuals with compromised immunity may benefit from Albendazole therapy

How can Microsporidiosis be Prevented?

Prevention of Microsporidiosis may be possible by filtering all forms of water that is meant for consumption (particularly in areas having low regulation for drinking water sources), as Microsporidia are water-borne parasites.

What is the Prognosis of Microsporidiosis? (Outcomes/Resolutions)

The prognosis of Microsporidiosis is as follows:

  • Treatment can be successful in decreasing infection by Microsporidia if it is addressed early. A complete eradication of Microsporidia with drug treatment is rare
  • Microsporidiosis often needs to be managed over a long period of time, and recurrent symptoms often need repetitive treatment
  • Without treatment, severe infection can lead to failure of organ systems resulting in death from the complications

Additional and Relevant Useful Information for Microsporidiosis:

  • The United States Environmental Protection Agency (EPA) has officially recognized microsporidia in the EPA Candidate Contaminate List (CCL)
  • Microsporidia spores are microscopic in size, have a round amorphous shape, and have a characteristic polar tubule protruding from the central body. The polar tubule of the microspore phylum is unique to the microsporidia parasites. No other known organisms present with this functionality
  • Only recently has Microsporidiosis been discovered to be present in immune-competent individuals (those with normally-functioning immune systems). However, this infection is still extremely rare in healthy individuals

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Helpful Peer-Reviewed Medical Articles:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Aug. 22, 2017
Last updated: Nov. 24, 2018