Taxonomy: Class Blastocystea
Animal: Blastocystis hominis 2 10.jpg
Sites: Gut
Blastocystis hominis - multi- vacuolar forms in faeces 5 - 20 microns with 1 - 4 nuclei (red dots) - see below centre towards 5 oclock, others also present. (trichrome stain) Avacuolar forms change to multi-vacuolar forms and then central vacuolar (CV) forms and then granular (G) forms (all 5-20 microns with 1-4 nuclei) when cultured or passed in faeces. The CV and granular forms were thought to be possibly the typical and only forms of B.hominis but they are not the forms in the colon. It is believed that the avacuolar forms, amoeboid forms and multivacuolar forms are the forms present in vivo and these develop to cysts in the external environment or develop into vacuolar forms if cultured. If the specimen is not examined fresh or fixed with PVA or formalin immediately on passing, these in vivo forms will have deteriorated and only the CV or G 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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