Question

Presence of ingested RBCs is a characteristic feature of
(a) Entamoeba histolytica
(b) Dientamoeba fragilis
(c) Entamoeba coli
(d) Iodamoeba butcheli

Answer 1

Hint:
Red blood cell ingestion is traditionally linked to E. histolytica, but it can happen with E. dispar on occasion, thus this is not a reliable way to tell them apart. Be aware that stained smears rarely show erythrophagocytosis.

Complete step by step answer:
The species Entamoeba histolytica and Entamoeba dispar are identical morphologically. E. histolytica/E. dispar cysts are spherical and typically measure 12 to 15 m (but they can be as large as 20 m) under bright-field microscopy. While an early cyst may only have one to three nuclei, a mature cyst contains four. The chromatin at the periphery is homogenous, fine, and equally dispersed. Sometimes you can find chromatoid bodies that are elongated and have sharply rounded ends. While clumped in early cysts, glycogen might be widespread or absent in adult cysts. The suggested methods for identifying E. histolytica/E. dispar include wet mount preparations and trichrome stained smears of stool samples. Trophozoites in trichrome-stained smears typically range in size from 15 to 20 m (but can reach as large as 60 m). The physical characteristics of trophozoites include the presence of a single nucleus with uniformly distributed chromatin on the nuclear membrane and a tiny, centrally positioned karyosome. There may be a few swallowed bacteria or debris in the coarsely granular cytoplasm. One way to identify E. histolytica is by looking for red blood cells within the cytoplasm of trophozoites. As ingested RBCs are uncommon, E. histolytica/E. dispar should be reported in the absence of this diagnostic feature.
Cysts often have 1 to 4 nuclei and measure 12 to 15 m (within a range of 10 to 20 m). There may also be chromatoid bodies with rounded blunt ends.

Option ‘A’ is correct

Note:
There is a quick cartridge that can detect E. histolytica/E. dispar antigens, but this assay cannot discriminate between the two. Giardia and Cryptosporidium antigens are also found using this assay. Prior to testing, stool samples shouldn't be concentrated and must be fresh or frozen. Test results acquired using this technique should be confirmed by extra research for suspect positives and negatives. There is no extra equipment required for this rapid and simple assay.