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Other Entamoeba , Amebae, and Intestinal Flagellates
In addition to Entamoeba histolytica ( Chapter 263 ), amebae that can be found in the human intestinal tract include other species of Entamoeba ( E. dispar, E. moshkovskii , E. bangladeshi, E. coli, E. hartmannii, E. polecki), Endolimax nana ( Chapter 262 ), and Iodamoeba bütschlii. Entamoeba gingivalis is found in the human mouth. These are generally nonpathogenic or of unclear pathogenicity and must be chiefly differentiated from the pathogenic E. histolytica . Many other species of Entamoeba are known to parasitize animals.
Pathogenic intestinal flagellates include Dientamoeba fragilis and Giardia duodenalis (syn. G. lamblia, G. intestinalis ) ( Chapter 265 ). Nonpathogenic intestinal flagellates include Chilomastix mesnili , Enteromonas hominis , Retortamonas intestinalis , and Pentatrichomonas hominis .
Entamoeba Histolytica/Entamoeba Dispar Group
E. histolytica, E. dispar, E. moshkovskii , and E. bangladeshi are morphologically indistinguishable under light microscopy; thus they are often referred to as the E. histolytica/E. dispar group. Trophozoites, with a diameter of 12–60 μm, have progressive motility and a central karyosome. Cysts are typically 10–20 μm in diameter and have four nuclei. , Historically, the presence of ingested erythrocytes in trophozoites was thought to be diagnostic of E. histolytica , but this also has been observed to a lesser degree in E. dispar . The pathogenic E. histolytica must be differentiated from the others with additional testing such as antigen or antibody detection, nucleic acid detection, or culture. , A number of stool antigen and serology assays, primarily to distinguish E. histolytica from E. dispar , are commercially available, and nucleic acid detection is available from the US Centers for Disease Control and Prevention (CDC). ,
Prevalence of individual species before the use of molecular techniques has been difficult to estimate and varies widely based on population and geography. E. dispar is more common than E. moshkovskii and E. bangladeshi .
Entamoeba dispar
E. dispar is a nonpathogenic intestinal commensal. Previously thought to be the nonpathogenic form of E. histolytica , it has now been accepted to be a separate species . Symptomatic E. dispar infection has not been definitively demonstrated in humans. However, it has been reported to cause disease in animal and in vitro models. , ,
Entamoeba moshkovskii
E. moshkovskii was first described in 1941 as an isolate from Moscow sewage and first linked to human disease in 1961 as a variant of E. histolytica . Although earlier studies of E. moshkovskii failed to show an association with clinical illness, in recent years, the organism has been associated with symptomatic gastrointestinal tract illness in humans and a mouse model of colitis.
Entamoeba bangladeshi
E. bangladeshi was identified in 2012 when a novel sequence was identified in diarrheal and surveillance samples positive for Entamoeba by culture or polymerase chain reaction (PCR) but negative for known species. Further investigation is required to determine the clinical significance of E. bangladeshi. ,
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