Microsporidia species

Disease / Pathology

The Microsporidia are a very large group of organisms that have been traditionally difficult to place within other groups of organisms because they are unicellular with some characteristics of more complex organisms yet falling in as a fungi in other characteristics. It is generally treated as a parasite in most text books/literature while identified as a fungus.

They generally produce spores that are highly resistant with a size range of between 1-4 um for most clinically important species. There are literally over a thousand species of Microsporidia yet only a small fraction that are known to cause human disease. To be more specific there have been to date about 15 species known to cause disease in humans.

When it does cause disease in humans it most commonly afflicts the immunocompromised such as those undergoing immunosuppressive therapy or HIV/AiDS patients. The location of the infection invariably depends on the species causing the infection as various species have more of a predilection for certain organ/body sites. The table below is a short list of some species and their predominant site of localization in the human host.

SpeciesKnown sites of localization
Anncaliia algeraeeyes, muscles
Anncaliia connorisystemic
Anncaliia vesicularummuscle
Encephalitozoon cuniculisystemic
Encephalitozoon hellemeyes]
Encephalitozoon intestinalissmall intestine
Encephalitozoon bieneusismall intestine, biliary tree
Microsporidium spp.eyes
Nosema ocularumeyes
Pleistophora ronneafieimuscle
Trachipleistophora anthropoptherasystemic
Trachipleistophora hominiseyes, muscle
Tubulinosema acridophagussystemic
Vittaforma corneaeeyes
Adapted from Han, B. and Weiss, L.M. 2017 Microsporidia obligate intracellular pathogens within the fungal kingdom. Microbiology Spectrum, 5(2)

Location in the Host

Microsporidia species location in infections varies with the species and the host. See table above.

Geographic Distribution

Microsporidia species with a worldwide distribution though various species are found more commonly in certain areas of the world then other areas.

Life Cycle

Life cycle of the Microsporidia – Image courtesy of CDC

Morphology & Diagnosis

Microsporidia species identification is dependent on the clinical symptoms in an immunocompromised person, site of infection, and staining of suspected biopsy material collected.


Encephalitozoon intestinalis stained with Calcofluor white – courtesy of CDC
Spores of E. cuniculi in a kidney biopsy specimen stained with Ryan’s modified trichrome. – courtesy of CDC
Microsporidia spores from a corneal section, stained with Giemsa. – courtesy of CDC