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Questions and Answers
What is the infective form of E.histolytica?
What is the infective form of E.histolytica?
Which route is the most common for the transmission of E.histolytica?
Which route is the most common for the transmission of E.histolytica?
In which part of the body does excystation of E.histolytica occur?
In which part of the body does excystation of E.histolytica occur?
Which of the following groups is specifically noted for higher risk of transmission of E.histolytica through the fecal-oral route?
Which of the following groups is specifically noted for higher risk of transmission of E.histolytica through the fecal-oral route?
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How do trophozoites of E.histolytica primarily obtain nutrients?
How do trophozoites of E.histolytica primarily obtain nutrients?
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What happens to cysts when they are exposed to desiccation?
What happens to cysts when they are exposed to desiccation?
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What is the typical outcome for the majority of E.histolytica infections in humans?
What is the typical outcome for the majority of E.histolytica infections in humans?
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What is the size range of trophozoites of E. histolytica?
What is the size range of trophozoites of E. histolytica?
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What contributes to the rare sexual transmission of E.histolytica?
What contributes to the rare sexual transmission of E.histolytica?
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What component is found in the endoplasm of the trophozoite?
What component is found in the endoplasm of the trophozoite?
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What is the main characteristic of the cyst of E. histolytica?
What is the main characteristic of the cyst of E. histolytica?
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Which of the following statements is true regarding the mature cyst of E. histolytica?
Which of the following statements is true regarding the mature cyst of E. histolytica?
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During the transformation from trophozoite to cyst, which of the following occurs first?
During the transformation from trophozoite to cyst, which of the following occurs first?
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What shape are the chromatoid bodies found in immature cysts of E. histolytica?
What shape are the chromatoid bodies found in immature cysts of E. histolytica?
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What feature primarily helps trophozoites of E. histolytica to move?
What feature primarily helps trophozoites of E. histolytica to move?
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What happens to the glycogen mass in the mature cyst of E. histolytica?
What happens to the glycogen mass in the mature cyst of E. histolytica?
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What is the most common site for an amoebic ulcer?
What is the most common site for an amoebic ulcer?
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What is the primary organ of locomotion in amebas?
What is the primary organ of locomotion in amebas?
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Which of the following is NOT a complication associated with intestinal amebiasis?
Which of the following is NOT a complication associated with intestinal amebiasis?
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Which of the following is a non-pathogenic intestinal amoeba?
Which of the following is a non-pathogenic intestinal amoeba?
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What characterizes a fulminant amoebic colitis?
What characterizes a fulminant amoebic colitis?
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What symptom is typically associated with amoebic infection?
What symptom is typically associated with amoebic infection?
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In which areas is Entamoeba histolytica more commonly found?
In which areas is Entamoeba histolytica more commonly found?
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Which type of amoebic ulcer results in scar formation after healing?
Which type of amoebic ulcer results in scar formation after healing?
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What percentage of the world’s population is affected by the disease caused by Entamoeba histolytica?
What percentage of the world’s population is affected by the disease caused by Entamoeba histolytica?
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Which group has a higher prevalence of infection by Entamoeba histolytica?
Which group has a higher prevalence of infection by Entamoeba histolytica?
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What is a potential result of the confluence of ulcers in intestinal amebiasis?
What is a potential result of the confluence of ulcers in intestinal amebiasis?
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What is the habitat of Entamoeba histolytica in humans?
What is the habitat of Entamoeba histolytica in humans?
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Which condition involves segment of intestine invaginating into an adjoining intestinal lumen?
Which condition involves segment of intestine invaginating into an adjoining intestinal lumen?
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Which of the following forms is NOT a morphology of Entamoeba histolytica?
Which of the following forms is NOT a morphology of Entamoeba histolytica?
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What indicates the presence of Entamoeba histolytica in histological examination?
What indicates the presence of Entamoeba histolytica in histological examination?
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Which demographic group is less likely to have severe cases of Entamoeba histolytica infections?
Which demographic group is less likely to have severe cases of Entamoeba histolytica infections?
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What can influence the variable clinical response to amebiasis?
What can influence the variable clinical response to amebiasis?
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Which factor does NOT contribute to the virulence of certain E.histolytica strains?
Which factor does NOT contribute to the virulence of certain E.histolytica strains?
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What is the characteristic form of lesions caused by E.histolytica invasion?
What is the characteristic form of lesions caused by E.histolytica invasion?
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What are common reasons for host susceptibility to E.histolytica infection?
What are common reasons for host susceptibility to E.histolytica infection?
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What is a common symptom associated with severe amebiasis?
What is a common symptom associated with severe amebiasis?
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Which of the following statements about E.histolytica is TRUE?
Which of the following statements about E.histolytica is TRUE?
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What role does stress play in the pathogenesis of amebiasis?
What role does stress play in the pathogenesis of amebiasis?
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Which term describes the phase of E.histolytica that invades the colonic mucosa?
Which term describes the phase of E.histolytica that invades the colonic mucosa?
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What characterizes an amoeboma?
What characterizes an amoeboma?
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Which cells are predominantly found in the granuloma of amoeboma?
Which cells are predominantly found in the granuloma of amoeboma?
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What complication can arise from chronic amoebiasis?
What complication can arise from chronic amoebiasis?
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What is the most common site for extraintestinal amoebiasis?
What is the most common site for extraintestinal amoebiasis?
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What is an amebic liver abscess (ALA)?
What is an amebic liver abscess (ALA)?
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How do amebae typically enter the liver in cases of amebic liver abscess?
How do amebae typically enter the liver in cases of amebic liver abscess?
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What can cause liver damage in amebic infections?
What can cause liver damage in amebic infections?
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Which of the following is NOT typically a result of amoebic intestinal infections?
Which of the following is NOT typically a result of amoebic intestinal infections?
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Study Notes
Intestinal Amoeba
- Intestinal amoeba are single-celled protozoa that change shape constantly.
- Their locomotion is aided by pseudopodia, which are cell extensions.
- Amoeba are classified by habitat: intestinal or free-living.
- Intestinal amoeba live in the large intestine of humans and animals.
- Free-living amoebas are small, free-living organisms, and some are opportunistic pathogens.
- Intestinal amoebas can be pathogenic (causing disease) or non-pathogenic.
- Entamoeba histolytica is a pathogenic intestinal amoeba.
- Entamoeba histolytica is found in the human colon's mucous and submucous layers of the large intestine.
- Entamoeba histolytica commonly infects tropical and subtropical regions, where poor socioeconomic status, poor nutrition, hygiene, and sanitation are more common issues in developing countries.
- Most Entamoeba histolytica infections are asymptomatic.
- Entamoeba histolytica is a common diarrheal pathogen in long-term travelers ( >6 months).
- The biggest burden of the disease is found in the tropics of China, Central and South America, and the Indian subcontinents, affecting 10% of the world's population.
- Some groups are at a higher risk for Entamoeba histolytica infections, like families of infected individuals, aboriginal people, male homosexuals, people in mental hospitals, prisons, and institutions for children.
Classification of Amoeba
- Amoebas are single-celled protozoa with constantly changing shapes.
- The presence of locomotion organs called pseudopodia is a key differentiator in this diverse group.
Entamoeba histolytica
- A worldwide distribution, more prevalent in the tropics and subtropics.
- Has three morphological forms: trophozoite, precyst, and cyst.
- Trophozoites are the vegetative form present in tissues. They are irregular in shape, averaging 20 µm in size and have pseudopodium for locomotion and containing cytoplasm made up of ectoplasm & endoplasm containing nucleus, food vacuoles and phagocytosed red blood cells.
- Precysts are a stage before encystment. These amoeba round up, extrude food vacuoles, have a smaller size (10–20 µm), have a glycogen vacuole and chromatoid bars.
- Cysts are a rigid, resistant form, measuring 10–20 µm, have a thick wall and are more resistant to gastric juice and unfavorable environmental conditions. They have 1–4 nuclei (mature cyst has four), chromatoid bars (aggregation of RNA), and glycogen mass.
Transmission
- Entamoeba histolytica is transmitted primarily through the fecal-oral route.
- Contaminated food or water containing mature cysts is a common source of infection.
- Food handlers, children and institutionalized groups are at an increased risk.
- Sexual contact is another possible route, especially among homosexual men in developed countries.
Life Cycle
- Entamoeba histolytica completes its life cycle in a single host (humans).
- The infectious form is the mature quadrinucleated cyst.
- This cyst resists chlorination, gastric acid, and desiccation. It can survive in moist environments.
- In the intestine, cysts excyst into trophozoites; these live in the gut lumen, mainly cecum, descending colon, and recto-sigmoid feeding on liquid substances and bacteria.
- Trophozoites encyst in the colon, which are excreted in the feces.
Pathogenesis
- Entamoeba histolytica infection is mostly asymptomatic.
- Under specific conditions, amoebas become invasive, causing tissue lysis, usually with host and parasite factors.
- Certain strains of E. histolytica have higher virulence; they produce proteolytic enzymes, cytotoxins, and cytolysins; often with surface adhesins.
- Factors that can influence E. histolytica invasiveness include factors like poor nutrition, stress during pregnancy, alteration of colonic flora and low resistance or weakened immune systems from various factors (e.g., diseases, drugs, etc.)
- Amoebic ulcers are a consequence of E. histolytica invasion.
- These ulcers can be either superficial (confined to the mucosal layers with no scarring) or deep (penetrating muscular layers with scar formation).
- The location of amoebic ulcers can vary in the ileocecal or sigmoid regions, or they can be widespread throughout the large intestine..
- Ulcers can coalesce and lead to sloughing of the mucosa and secondary bacterial infection.
- Severe complications, like fulminant colitis or perforation, also result from infection.
- Extraintestinal amoebiasis involves trophozoite spread to other organs like the liver which causing abscesses (usually in the upper right lobe of the liver).
Diagnosis
- Diagnosis of E. histolytica relies on various methods:
- Microscopic examination of stool samples for cysts or trophozoites.
- Molecular diagnostic tools like PCR.
- Serological testing for antibodies is helpful for identifying invasive amoebiasis through the detection of cysts or trophozoites in stool or mucosal scrapings.
- Sigmoidoscopy with mucosal scrapings for visualization and direct examination of the trophozoites.
Treatment
- The primary treatments for amebiasis generally involve metronidazole or tinidazole.
- Supportive care, including fluid and electrolyte replacement, is often necessary.
Prevention
- Public health measures, including safe food handling, adequate sanitation and hygiene practices, are vital strategies for preventing transmission.
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Description
This quiz explores the characteristics and classifications of intestinal amoeba, focusing on their biological functions and the implications of specific species like Entamoeba histolytica. Understand their role as both pathogenic and non-pathogenic organisms, especially in human health. Key factors influencing infection rates in various regions are also considered.
