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Questions and Answers
What method do Amoebozoa primarily use for locomotion and food capture?
What method do Amoebozoa primarily use for locomotion and food capture?
What is the primary mode of reproduction in Amoebozoa?
What is the primary mode of reproduction in Amoebozoa?
Which species is known to cause amoebic dysentery?
Which species is known to cause amoebic dysentery?
What is a characteristic feature of Entamoeba histolytica cysts?
What is a characteristic feature of Entamoeba histolytica cysts?
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What role do the trophozoites play in the life cycle of Entamoeba histolytica?
What role do the trophozoites play in the life cycle of Entamoeba histolytica?
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What percentage of Entamoeba histolytica infections result in noticeable symptoms?
What percentage of Entamoeba histolytica infections result in noticeable symptoms?
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In what type of environments does Entamoeba histolytica predominantly occur?
In what type of environments does Entamoeba histolytica predominantly occur?
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What metabolic process characterizes the obligate anaerobes of the Entamoeba histolytica species?
What metabolic process characterizes the obligate anaerobes of the Entamoeba histolytica species?
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What is the primary mode of transmission for Entamoeba histolytica cysts?
What is the primary mode of transmission for Entamoeba histolytica cysts?
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What type of strain of Entamoeba histolytica primarily causes severe symptoms?
What type of strain of Entamoeba histolytica primarily causes severe symptoms?
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What is a significant factor in the virulence of Entamoeba histolytica?
What is a significant factor in the virulence of Entamoeba histolytica?
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What is the result of necrosis due to the invasion of virulent trophozoites in the intestine?
What is the result of necrosis due to the invasion of virulent trophozoites in the intestine?
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What condition can result from the coalescence of multiple ulcers caused by Entamoeba histolytica?
What condition can result from the coalescence of multiple ulcers caused by Entamoeba histolytica?
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What is a potential consequence of fibrous scar tissue formation following Entamoeba histolytica infections?
What is a potential consequence of fibrous scar tissue formation following Entamoeba histolytica infections?
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Which of the following can lead to secondary infections in patients with Entamoeba histolytica?
Which of the following can lead to secondary infections in patients with Entamoeba histolytica?
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What is the mechanism through which trophozoites of Entamoeba histolytica invade gut tissue?
What is the mechanism through which trophozoites of Entamoeba histolytica invade gut tissue?
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Which of the following describes an asymptomatic strain of Entamoeba histolytica?
Which of the following describes an asymptomatic strain of Entamoeba histolytica?
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What is a primary target organ for extraintestinal infection by Entamoeba histolytica?
What is a primary target organ for extraintestinal infection by Entamoeba histolytica?
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Which antibiotic is commonly used to treat infections caused by Entamoeba histolytica?
Which antibiotic is commonly used to treat infections caused by Entamoeba histolytica?
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How does intestinal dysbiosis affect a host's susceptibility to Entamoeba histolytica?
How does intestinal dysbiosis affect a host's susceptibility to Entamoeba histolytica?
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What structural feature of Entamoeba histolytica contributes to its blood-feeding behavior?
What structural feature of Entamoeba histolytica contributes to its blood-feeding behavior?
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Which portion of the large intestine is most affected by the pathogenesis of Entamoeba histolytica?
Which portion of the large intestine is most affected by the pathogenesis of Entamoeba histolytica?
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Study Notes
Amoebozoa Lineage
- Locomotion and food capture achieved through pseudopodia.
- Heterotrophic, consuming bacteria, algae, and other protozoa.
- Found in freshwater, saltwater, and soil environments.
- Food ingested by phagocytosis followed by food vacuole formation.
- Asexual reproduction through mitotic fission.
- Parasitic forms infect humans and primates.
- Parasitic intestinal forms are anaerobic.
Entamoeba Genus
- Includes species like E. histolytica, E. dispar, E. moshkovskii, E. coli, and E. gingivalis.
- E. histolytica is the causative agent of amoebic dysentery.
- Dysentery is characterized by frequent stools containing blood and mucus.
- Symptoms can include cramping, fever, abdominal pain, and weight loss.
- E. histolytica is estimated to cause 50 million cases annually and 40,000-100,000 deaths.
- Only 10-20% of infections result in disease; most individuals are asymptomatic carriers.
- Parasite virulence factors, host genetics, intestinal microbiota, and immune responses influence disease development in hosts.
- Occurs in densely populated areas with unsanitary conditions.
Entamoeba histolytica
- Lacks a contractile vacuole and mitochondria; contains a mitosome.
- An obligate anaerobe with fermentative metabolism.
- Nucleus contains a karyosome, a condensed region of chromatin.
- Mature cysts (10-15 μm, 4 nuclei) possess bar-shaped chromatoidal bodies, which are ribosome stores.
- Cysts have a highly resistant chitin wall.
- Diagnosis involves microscopic examination of stool samples for cysts and trophozoites but DNA sequence analysis is considered the most reliable method.
Entamoeba histolytica Life Cycle
- Two main stages:
- Trophozoite: actively growing, feeding, and replicating.
- Cyst: transmission stage, resistant to environmental conditions.
- Trophozoites reproduce asexually via binary fission and differentiate into cysts.
- E. histolytica infections are primarily restricted to humans but some reports suggest other mammals may be susceptible.
Entamoeba histolytica Transmission
- Transmission occurs via the fecal-oral route through infective cysts.
- Remember the "5 F's": flies, fingers, feces, food, and fomites.
Entamoeba histolytica Life Cycle (Detailed)
- Ingested cysts reach the small intestine, undergo multiple cell divisions, and release 8 trophozoites.
- Trophozoites migrate to the large intestine (colon) and multiply in the lumen.
- They can also invade the gut wall, leading to amoebic dysentery.
- E. histolytica can cause secondary extraintestinal infections by entering the bloodstream.
- These extraintestinal infections commonly affect the liver, lungs, and sometimes the brain.
- Amoebic colitis and dysentery are usually treated with the antibiotic metronidazole.
Entamoeba histolytica Pathogenesis
- Disease severity ranges from asymptomatic to severe amoebic colitis or dysentery.
- Non-invasive (avirulent) strains of E. histolytica remain in the intestinal lumen and are asymptomatic or cause mild gastrointestinal symptoms.
- These strains can potentially evolve into invasive strains capable of mucosal penetration.
- Invasive (virulent) strains invade epithelial cells lining the intestine and spread into underlying tissues, forming flask-shaped ulcers and causing bleeding.
Entamoeba histolytica Virulence Factors
- Adherence to host mucosal cells is mediated by a parasite Gal/GalNAc lectin.
- This lectin binds to host galactose (Gal) and N-acetyl-D-galactosamine (Gal/NAc) residues with high affinity.
- Host cell glycoproteins lacking galactose residues show resistance to cytotoxicity.
- The Gal/GalNAc lectin is a heterodimer with a carbohydrate recognition domain (CRD).
- The CRD binds to host cell glycoproteins (e.g., mucins) containing Gal or Gal/NAc.
- The Gal/GalNAc lectin prevents complement-mediated lysis and allows the parasite to adhere to the host mucosa.
- Adhesion ability significantly contributes to the parasite's virulence.
Entamoeba histolytica Pathogenesis (Continued)
- Invasive (virulent) strains:
- Early stages exhibit small areas of necrosis or ulcers, resulting in stools with blood and mucus (amoebic colitis).
- Trophozoites spread laterally and downwards, destroying epithelial cells and creating characteristic flask-shaped ulcers.
- Hematophagous trophozoites replicate rapidly, expanding the ulcers and leading to fulminating necrotic colitis.
Entamoeba histolytica Pathogenesis (Continued)
- Large numbers of ulcers merge to cause mucosal necrosis, with parts of the intestinal wall sloughing off.
- Secondary bacterial invasion of ulcers aggravates damage, leading to further blood and fluid loss.
- Healing ulcers are replaced by fibrous scar tissue, reducing gut elasticity and impairing peristalsis.
- Amoebic granulomas can form and are often mistaken for tumors.
Entamoeba histolytica Virulence Factors & Pathogenesis
- Non-invasive trophozoites stay on the luminal surface, ingesting bacteria and cell debris without invading the mucous layer.
- Invasive trophozoites erode the mucous layer, kill enterocytes, and invade the lamina propria and submucosal layers.
- Parasite-derived enzymes degrade the host extracellular matrix, leading to muscle and serous layer perforation, peritonitis, and systemic infection (dissemination).
- Virulence factors, host immune defense, and gut microbiota composition play intricate roles in regulating parasite virulence.
- Intestinal dysbiosis increases the risk of severe disease outcomes.
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Description
Explore the Amoebozoa lineage and the important characteristics of the Entamoeba genus. Learn about their locomotion, reproduction, and the impact of parasitic species like E. histolytica on human health. This quiz covers key concepts and facts about these intriguing protozoa.
