Amoebiasis: Advances in Diagnosis, Treatment, Immunology Features and the Interaction with the Intestinal Ecosystem

Abstract

This review of human amoebiasis is based on the most current knowledge of pathogenesis, diagnosis, treatment, and Entamoeba/microbiota interactions. The most relevant findings during this last decade about the Entamoeba parasite and the disease are related to the possibility of culturing trophozoites of different isolates from infected individuals that allowed the characterization of the multiple pathogenic mechanisms of the parasite and the understanding of the host-parasite relationship in the human. Second, the considerable advances in molecular biology and genetics help us to analyze the genome of Entamoeba, their genetic diversity, and the association of specific genotypes with the different amoebic forms of human amoebiasis. Based on this knowledge, culture and/or molecular diagnostic strategies are now available to determine the Entamoeba species and genotype responsible for invasive intestinal or extraintestinal amoebiasis cases. Likewise, the extensive knowledge of the immune response in amoebiasis with the appearance of new technologies made it possible to design diagnostic tools now available worldwide. Finally, the understanding of the interaction between the Entamoeba species and the intestinal microbiota aids the understanding of the ecology of this parasite in the human environment. These relevant findings will be discussed in this review.

Keywords: advanced diagnosis and treatment; amoebiasis; intestinal microbiota interaction; pathogenesis.

Figure 1

The life cycle of E. histolytica/E. dispar. Mature cysts (green) are swallowed along with food and water. The cysts pass through the stomach, but if the stomach is alkaline or when the cyst reaches the small intestine the cyst wall is damaged by trypsin, excystation starts (light blue). Trophozoites emerge (blue) and colonize the caecum and colon. Trophozoites are the infective amoeboid form which multiply by binary fission and can migrate to other tissues causing an extraintestinal invasion (red) or initiate encystment forming immature cysts and, finally, a mature cyst (yellow) to start a new cycle. (a) Mature cyst stained with 4% Lugol’s solution (100× magnification); (b) Mature cyst without staining (100×); (c) Trophozoite observed with differential interference contrast (DIC) (100×); (d) Trophozoites of E. histolytica with phagocyted erythrocytes (DIC) (40×) in Ximénez et al. [11].

Figure 2

(a) Intestinal flask-shaped ulcers observed through rectosigmoidoscopy examination. Arrows indicate colonic ulcers. (b) Large bowel necropsy specimen from a case of fulminant amoebic colitis. Arrows indicate hemorrhagic ulcers and important intestinal mucosa necrosis. (c) Necropsy specimen of liver abscesses. Arrows indicate the three large abscesses. (d) Intestinal biopsy obtained from the edge of a flask-shaped ulcer where large numbers of trophozoites (HE and PAS stained, 60×) are visible. (e) Biopsy obtained from the edge of an amoebic liver abscess (HE and PAS stained, 20×). Notice the presence of trophozoites, hepatocytes, and many inflammatory cells. Courtesy Doctor Ruy Pérez-Tamayo in Ximénez et al. [11].