INTRODUCTION
Entamoeba histolytica (E. histolytica) remains a major cause of invasive intestinal disease in tropical regions. Although the Entamoeba genus comprises numerous commensal species, recent studies have suggested that Entamoeba dispar (E. dispar) and Entamoeba moshkovskii (E. moshkovskii) may also induce gastrointestinal symptoms.1 Here, the microscopic visualization of trophozoites from standard axenic culture HM1:IMSS (Human isolate, Instituto Mexicano del Seguro Social) and a patient sample are presented using different stains and scanning electron microscopy (SEM) (Figures 1–3).2,3 A male patient presented to the out patient department with a 14-day history of abdominal pain and loose stools. A same-day stool examination revealed trophozoites of an E. histolytica/E. dispar/E. moshkovskii complex, but no other intestinal parasites were detected (Figure 2). The patient was started on anti-amoebic therapy. Erythrophagocytosis was observed in cultured trophozoites, a feature strongly associated with invasive E. histolytica. Scanning electron microscope images revealed prominent lobopodial extensions (Figure 3). Polymerase chain reaction testing confirmed infection with E. histolytica.4
Figure 1.
Entamoeba histolytica trophozoites from an axenic culture (A–D; 40× magnification). (A) trophozoites; (B) trophozoite exhibiting erythrophagocytosis; (C) single trophozoite exhibiting amoeboid movement and lobopodium; (D) iodine stain. The scale bar for all the images is 5 µm.
Figure 3.
Scanning electron micrographs showing (A and B) Entamoeba histolytica trophozoite (axenic culture) with visible lobopodium. (C) Entamoeba species trophozoite (stool sample).
Figure 2.
Patient stool sample with trophozoites of Entamoeba species (species-level identification is not possible using microscopy alone; 40× magnification). (A) Wet mount, (B and C) iodine mount, (D) methylene blue stain, (E) Entamoeba coli, (F) Iodamoeba butschlii. The scale bar for all the images is 10 µm.
In the authors’ experience, iodine mount and methylene blue stain are better suited for identifying trophozoites, despite reduced motility compared with wet mount (Figure 2). Entamoeba coli and Iodamoeba butschlii, which are often mistaken for E. histolytica on routine microscopy, are shown in Figure 2. Although SEM is not used in routine clinical diagnosis, it is presented here for morphological illustration. Although microscopy alone cannot differentiate among the three species, it remains essential for rapid detection in endemic regions. Overreliance on advanced diagnostic erodes these critical microscopy skills, risking patient care and public health.5
ACKNOWLEDGMENTS
The authors gratefully acknowledge the Department of Science and Technology for providing Devyani Sharma with a fellowship. The American Society of Tropical Medicine and Hygiene (ASTMH) assisted with publication expenses.
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