Taxonomy: Class Blastocystea
Animal: Blastocystis hominis 8 12.jpg
Sites: Gut
Blastocystis hominis -avacuolar forms- Trichrome stain. -- see just off centre and below that (these forms inhabit the colon along with amoeboid forms but may be overlooked because of their small size, 5 microns or because they degenerate after passage). They have 1 or 2 nuclei and may transform into amoeboid forms. They change to a multi-vacuolar form and then a central vacuolar form and then a granular form (all 5-20 microns with 1-4 nuclei) when cultured or passed in faeces. These CV and G forms were at first thought to be the typical and only forms of B.hominis but are now known not to be the forms found in the colon. Unless the specimen is examined fresh or fixed with PVA or formalin immediately on passing, the in vivo forms ( avacuolar, amoeboid and multi- vacuolar forms) will have deteriorated and only the CV or granular forms will be seen in wet preparations, cysts will be missed if a stained smear is not examined due to their small size - 5 microns.

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