Amoebozoa and Entamoeba Genus Quiz

Amoebozoa Lineage

• Amoebas are heterotrophic organisms found in freshwater, saltwater, and soil.
• They capture food and move by extending pseudopodia.
• They reproduce asexually via mitotic fission.
• Some amoebas are parasitic and infect humans and other primates.

Entamoeba Genus

• Entamoeba histolytica is the causative agent of amoebic dysentery.
• Amoebic dysentery is characterized by bloody and mucous diarrhea.
• It can also cause abdominal pain, fever, cramping, and weight loss.
• E. histolytica is estimated to cause 50 million cases and 40,000-100,000 deaths annually.
• Only 10-20% of E. histolytica infections result in disease.
• E. histolytica pathogenesis is influenced by parasite virulence factors, host genetics, intestinal microbiota, and immune responses.
• E. histolytica is commonly found in areas with large populations living in unsanitary conditions.

Entamoeba Histolytica

• E. histolytica is an obligate anaerobic organism.
• It does not have a contractile vacuole or mitochondria but has a mitosome.
• E. histolytica has a characteristic karyosome within its nucleus.
• E. histolytica cysts are resistant to environmental conditions.
• E. histolytica cysts are 10-15 µm with 4 nuclei and bar-shaped chromatoidal bodies made of ribosomes.
• E. histolytica cysts are diagnosed by microscopic examination of stool samples, but DNA sequencing is the most accurate.

Entamoeba Histolytica Life Cycle

• Entamoeba histolytica life cycle has two main stages: trophozoite and cyst.
• Trophozoites are actively growing, feeding, and reproducing stages.
• Cysts are transmission stages, resistant to environmental conditions.
• Trophozoites reproduce asexually via binary fission and differentiate into cysts.
• Transmission is through the fecal-oral route.
• Ingested cysts reach the small intestine and differentiate into trophozoites.
• Trophozoites migrate to the large intestine (colon) and multiply in the lumen.
• Trophozoites can invade the gut wall and cause amoebic dysentery.
• E. histolytica can invade other organs like the liver, lungs, and brain through the bloodstream.
• Amoebic dysentery is treated with metronidazole.

Pathogenesis Caused by E. Histolytica

• E. histolytica infection can range from asymptomatic to severe amoebic colitis or dysentery.
• Non-invasive (avirulent) strains of E. histolytica remain within the intestine and cause mild symptoms or are asymptomatic.
• Invasive (virulent) strains of E. histolytica invade epithelial cells lining the intestine and spread into underlying tissue layers.
• Invasive strains cause flask-shaped ulcers and bleeding in the intestine.
• Invasive strains can also invade other organs through the circulatory system, causing extraintestinal amebiasis.

Entamoeba Histolytica Adherence

• Adherence to host mucosal cells is mediated by a parasite Gal/GalNAc lectin.
• The parasite Gal/GalNAc lectin binds to host galactose (Gal) and N-acetyl-D-galactosamine (Gal/NAc) residues.
• Host cell glycoproteins lacking galactose residues are more resistant to cytotoxicity.
• The Gal/GalNAc lectin is a heterodimer.
• The parasite Gal/GalNAc lectin prevents complement-mediated lysis and allows adherence to the host mucosa.

E. Histolytica Pathogenesis

• Invasive strains of E. histolytica cause small areas of necrosis or ulcers, resulting in bloody and mucous diarrhea, which is called amoebic colitis.
• Trophozoites spread laterally and downwards, killing epithelial cells and resulting in characteristic flask-shaped ulcers.
• Hematophagous trophozoites replicate at high rates, expanding ulcers and causing fulminating necrotic colitis.
• Large numbers of ulcers coalesce to cause mucosal necrosis.
• Parts of the intestinal wall slough off, causing amoebic granuloma formation.
• Amoebic granulomas are often misidentified as tumors.

E. Histolytica Virulence Factors and Pathogenesis Regulation

• Non-invasive trophozoites remain on the luminal surface and ingest bacteria and cellular debris.
• Invasive trophozoites erode the mucous layer, kill enterocytes, and invade the lamina propria and submucosal layers.
• Parasite-derived enzymes break down the host extracellular matrix, leading to perforation of the muscle and serous layers, causing peritonitis.
• This can lead to infection spread through the circulatory system and extraintestinal infections.
• Virulence regulation is complex and involves parasite-derived virulence factors, host immune defense, and gut microbiota composition.
• Intestinal dysbiosis increases susceptibility to severe disease outcomes.

Test your knowledge on the Amoebozoa lineage and the Entamoeba genus. Learn about the characteristics, reproduction, and pathogenicity of amoebas, particularly Entamoeba histolytica, the causative agent of amoebic dysentery. Explore how these organisms affect human health and their environmental conditions.