Microsporidia are obligate intracellular parasites.

Their typical size ranges from 1.5-5 mm wide by 2-7 mm long. The organisims found in humans are normally smaller and range in size from 1.5-2 mm.

Five genera have been recognized in humans to date and classification depends on the "gold standard" method of identification electron microscopy.

Other methods available for identification are modified trichrome stain, touch preparation stained by Giemsa, paraffin embedded tissues and flourescent staining.

Enterocytozoon species

Many objects within stool material are oval and stain pinkish with the trichrome stain and could be confused with the species found in stool (E.bieneusi at right).

The organisms tend to clump together and they do not chain.

Encephalitozoon species

This species, E.cuniculi, tends to be associated with infection of the central nervous system and would have less chance of being mistaken for bacteria. They are also larger than Entercytozoon bieneusi.