Amoebiasis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Yazan Daaboul, M.D.; Serge Korjian M.D.

Overview

Transmission

  • E. histolytica cyst is usually transmitted by the fecal-oral route through contaminated drinking water or food)
  • E. histolytica cyst may also be transmitted indirectly through direct contact with infected individuals.

Pathogenesis

  • Following transmission, E. histolytica trophozoites inhabit in the large intestine of the human host.
  • In the large intestine, the trophozoites invades the intestinal mucosa into the bloodstream. Simultaneously, they form resistant cysts in the large intestines that are then excreted in human stools.
  • Once in the bloodstream, the trophozoite migrates into the portal circulation and develops amebic liver abscess.[1]

Invasion of Intestinal Mucosa

  • E. histolytica trophozoites secrete proteases, which induce the release of mucin from goblet cells, resulting in glandular hyperplasia.[1]
  • E. histolytica is also thought to contain glycosidases that cleave glycsolyated mucin molecules, resulting in mucin degradation.[2][3]
  • Once the mucin layer is degraded, E. histolytica then adheres to plasma membrane of enterocytes and uses lectins, amebapores, and proteases to cause damage by a characteristic "hit and run" phenomenon.[1]
  • Lectin: responsible for adhesion of the parasite on Gal-GalNAc residues on enterocytes
  • Amebapore: Protein that forms channels that induce cytolysis in a process similar to perforin-mediated cytolysis of cytotoxic T-cells
  • Protrease: Enzymes that metabolize cellular proteins
  • As the trophozites creates interglandular lesions and degrades the extracellular matrix, it is propelled forward by locomotion.[1][4][5]

Activation of Host Immune System

  • As the trophozoites invade, IL-8 and TNF-alpha secretion is upregulated, and the host immune cells are activated.[6][7]
  • Neutrophils migrate to the site of invasion and contribute to the inflammatory damage induced by E. histolytica, but are generally incapable of destroying the organism. The mechanism may which E. histolytica evades neutrophils is unknown.[6][7][1]
  • Once neutrophils are recruited, macrophages and eosinophils are also activated.[1]

Pathology

Gross Pathology

On gross pathology, the following findings may be present in patients with amebiasis:[1]

  • Wavy surface epithelium (results from focal release of mucin and spasm of the muscular layer)
  • Nodular and/or irregular ulcers in the cecum (most common), sigmoid colon, and rectum. Early ulcers are usually in the interglandular epithelium.
  • Nodular: small (sub-centrimetric), rounded, elevated lesions with necrotic center and edematous rim
  • Irregular: large (1-5 cm), shallow with broad elevated margins

Note: the mucosal folds may occasionally hide small colonic ulcers (false-negative results)

Microscopic Pathology

  • On microscopic pathology, amebiasis is characterized by a flask ulcer (deep, microhemorrhagic ulceration involving the submucosa), which is a characteristic of advanced disease.[1]
  • Additional findings may be present in patients with amebiasis:[1]
  • Interglandular ulceration
  • Hyperemia
  • Thickened mucosa
  • Reactive glandular hyperplasia
  • Stromal edema
  • Infiltration of neutrophils, eosinophils (rare), and macrophages
  • Lymphoid aggregates
  • Detection of amebas on surface exudate
  • Tissue necrosis, usually fibrinoid (advanced lesion)
  • Formation of granulation tissue (advanced lesion)

Gallery

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Espinosa-Cantellano M, Martínez-Palomo A (2000). "Pathogenesis of intestinal amebiasis: from molecules to disease". Clin Microbiol Rev. 13 (2): 318–31. PMC 100155. PMID 10756002.
  2. Müller FW, Franz A, Werries E (1988). "Secretory hydrolases of Entamoeba histolytica". J Protozool. 35 (2): 291–5. PMID 2456386.
  3. Spice WM, Ackers JP (1998). "The effects of Entamoeba histolytica lysates on human colonic mucins". J Eukaryot Microbiol. 45 (2): 24S–27S. PMID 9561780.
  4. Talamás-Rohana P, Meza I (1988). "Interaction between pathogenic amebas and fibronectin: substrate degradation and changes in cytoskeleton organization". J Cell Biol. 106 (5): 1787–94. PMC 2115038. PMID 2897372.
  5. Espinosa-Cantellano M, Martínez-Palomo A (1994). "Entamoeba histolytica: mechanism of surface receptor capping". Exp Parasitol. 79 (3): 424–35. PMID 7957761.
  6. 6.0 6.1 Eckmann L, Reed SL, Smith JR, Kagnoff MF (1995). "Entamoeba histolytica trophozoites induce an inflammatory cytokine response by cultured human cells through the paracrine action of cytolytically released interleukin-1 alpha". J Clin Invest. 96 (3): 1269–79. doi:10.1172/JCI118161. PMC 185748. PMID 7657801.
  7. 7.0 7.1 Yu Y, Chadee K (1997). "Entamoeba histolytica stimulates interleukin 8 from human colonic epithelial cells without parasite-enterocyte contact". Gastroenterology. 112 (5): 1536–47. PMID 9136832.
  8. 8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 "Public Health Image Library (PHIL)".


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