Taxonomy: Class Blastocystea
Animal: Blastocystis hominis 8 10 .jpg
Sites: Gut
Blastocystis hominis Cyst (at 4 oclock from CV) & Vacuolar, CV form (in centre) - trichrome stain. Cysts arise from the multivacuolar forms in the colon, is about 5 microns wide, usually one nucleus, thick cyst wall and very small vacuoles. Vacuolar form has a central vacuole with 1 - 4 nuclei and 5 - 20 microns wide). 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 - light microscopy being the usual way to examine faecal samples.

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