Taxonomy: Class Blastocystea
Animal: Blastocystis hominis 4 09.jpg
Sites: Gut
Blastocystis hominis cyst (just off centre) . Cysts arise from the avacuolar and multivacuolar forms in the colon, is about 5 microns wide, 1 or more nuclei, thick cyst wall and very small vacuoles. This may be the transmissible stage but this has not been proven (Trichrome stain of faecal preparation). 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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