Taxonomy: f. Entamoebidae
Animal: Entamoeba histolytica 3 15.jpg
Entamoeba histolytica trophozoite containing ingested red cells which is diagnostic. Trophozoite is 12 - 60 microns (invasive forms greater than 20). Single nucleus with fine peripheral chromatin and small compact karyosome in faecal smear stained with Trichrome. Clinical notes and travel history are essential in determining tests required. If the faeces is not examined within 1/2 hour of passing to see motile trophozoites OR fixed immediately with PVA fixative, protozoan parasites deteriorate and may be missed; this is particularly relevant for liquid or soft stools specimens from people who have travelled to areas of poor hygiene and children less than 10 years. Zn PVA may be preferred to Hg PVA as a less toxic fixative although morphology not as well defined but care in handling is still important using 1:3 -faeces:fixative (refer to Garcia&Bruckner 1997 for full discussion of preservation and examination of parasites - see Bibliography) . It is essential for identification to examine stained (FeHX or Trichrome) smear as well as saline and iodine preparations as this was found to increase detection rates by up to 3 times (RE Pugh, unpublished). Preferably 3 specimens collected on alternate days over 10 days should be examined; if amoebiasis is suspected, 6 specimens over 14 days should be examined. To ensure cure, specimens should be examined 3-4 weeks after treatment. Serological tests, biopsies and various molecular tests may also be useful.
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