Intestinal Amoebae Multiple Question & Answers

Question 1. Which of the following fits to the life cycle in the picture given below?

1. Balantidium coli
2. E. histolytica
3. Ancylostoma duodenale
4. Enterobius vermicularis

Answer. (2) (E. histolytica)

• This above life cycle belongs to E. histolytica
• Ingestion of quadri-nucleated cyst → develops to trophozoites → multiply in large intestine→ develops to precyst → cyst (immature) → quadri-nucleated cyst (mature) passes in stool.

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Question 2. Small amounts of thin stools with mucus, not adherent to the container. The patient has subjective feelings of fever and lower abdominal pain, with few leukocytes in stool.

1. Which of the following is likely to be the causative agent?
2. Giardia lamblia
3. Entamoeba histolytica
4. Staphylococcus aureus
5. Clostridium perfringens

Answer. (2) (Entamoeba histolytica)

• Thin stools with mucus, not adherent to the container is suggestive of amoebic dysentery
• Fever and lower abdominal pain can be seen as a feature of amoebic colitis

Question 3. The patient presents with diarrhea, associated with blood, stool, mucous, and fever. What is your likely diagnosis?

1. Giardia lamblia
2. E. histolytica
3. Salmonella Typhi
4. Isospora species

Answer. (2) (E. histolytica)

• E.histolytica the only agent among the options given in the question that causes diarrhea with blood and mucous. Blood in stool is not a feature of Giardia, Salmonella Typhi or Isospora.

Question 4. Ingested RBCs are seen in

1. Entamoeba histolytica
2. Entamoeba dispar
3. Balantidium coli
4. Entamoeba moshkovskii

Answer. (1) (E. histolytica)

• RBCs inside the trophozoites are a sign of invasion; a feature seen in pathogenic Entamoeba,i.e. E.histolytica.

Question 5. Which can differentiate E.histolytica from E.dispar?

1. 170 kDa antigen
2. Cyst
3. Trophozoite

Answer. (1) (170 kDa antigen)

Question 6. A 23-year-old male presented with abdominal pain and bloody diarrhea of one week duration. The following colonoscopic biopsy is diagnostic of infection with:

1. Giardiasis
2. Amoebiasis
3. Enterobius
4. Severe bacterial infection

Answer. (2) (Amoebiasis)

• A history of bloody diarrhea, and tiny round trophozoites seen in colonoscopic biopsy confirms the diagnosis as Intestinal amoebiasis.

Question 7. All are true about Entamoeba histolytica except:

1. Stool trophozoites are essential for the diagnosis
2. Most (85%) are asymptomatic
3. Cause disease in the brain
4. Cause disease in the liver

Answer. (1) (Stool trophozoites are essential for diagnosis)

• Stool trophozoites are usually found in the acute stage of amoebic dysentery and indicate active infection but they soon disappear and are not found in later stages of dysentery or carriers or in invasive amebiasis.
• Hence stool trophozoites are NOT essential for diagnosis; however, their presence confirms an active stage of amoebic dysentery.
• Confirmation of the diagnosis can also be done by amoebic PCR or detection of lectin antigen in stool.

Other options:

• Entamoeba histolytica infection is mostly asymptomatic
• Invasive amoebiasis: The liver is the most common site, but can also infect other sites such as the lungs and brain.

Question 8. Which of the following statements about amoebiasis is False?

1. Amoebic dysentery: Flask-shaped ulcer
2. Entamoeba coli can be pathogenic
3. Liver is the MC extra intestinal site

Answer. (2) (Entamoeba coli can be pathogenic)

9. The virulence factor that is responsible for adherence of Entamoeba histolytica to intestinal mucosa is:

1. Ionophore-like protein
2. Amoebic lectin
3. Phosphatase
4. Proteinase

Answer. (2) (Amoebic lectin)

Amoebic lectin antigen is the principal virulence factor of Entamoeba histolytica that is responsible for adherence to large intestinal mucosa.

Question 10. The most common site for Amebiasis is:

1. Sigmoid colon
2. Transverse colon
3. Cecum
4. Hepatic flexure

Answer. (3) (Cecum)

• The most common site for Amebiasis is the ileocecal region followed by the Sigmoid colon or may be generalized involving the whole of the large intestine.

Question 11. Investigation of choice for amebiasis is:

1. ELISA
2. Colonoscopy
3. Microscopy
4. Microscopy + ELISA

Answer. (4) (Microscopy + ELISA)

• ‘Microscopy, often combined with serologic testing, remains the standard diagnostic approach in many hospitals and clinics worldwide for the diagnosis of amebiasis.’
• Stool Microscopy—done to demonstrate:
  • Trophozoites: Indicates active infection
  • Quadrinucleated cysts: Indicates carrier state
• Microscopy is poorly sensitive (25–60% with a single sample) but the sensitivity increases to 85–95% when three stool samples are examineIt cannot differentiate between E.histolytica and other Entamoeba histolytica subspecies such as E. dispar and E.moshkovskii.
• ELISA detecting 170 kDa of lectin antigen in stool shows > 95% sensitivity and specificity. It can also differentiate pathogenic E. histolytica (lectin antigen positive) and nonpathogenic E.dispar ((lectin antigen negative).
• Polygenic culture: 50–70% sensitivity and 100% specificity (gold standard). Serves as a research tool but not available for clinical use.
• PCR assay for DNA in stool samples is currently the most sensitive and specific method for identifying E. histolytica infection and has become a valuable epidemiologic and research tool.

Question 12. A number of nuclei present in the mature cyst of E. histolytica is:

1. 1
2. 2
3. 4
4. 8

Answer. (3) (4)

• Mature cyst of E. histolytica: Contains four nuclei
• Mature cyst of E. coli: Contains eight nuclei

Question 13. The most common cause of dysentery in adults is:

1. Crypto parvum
2. Giardia
3. Strongoloides
4. Entamoeba histolytica

Answer. (4) (Entamoeba histolytica)

• Entamoeba histolytica is one of the most common cause of dysentery in man
• Other Agents of dysentery include: Bacterial dysentery (e.g. Shigella and Campylobacter and Vibrio parahemolyticus), Parasitic causes (schistosomiasis, Trichuris and Balantidium coli)
• In Cryptosporidium parvum, Giardia, and Strongoloides infection: Diarrhea is the chief manifestation (not dysentery).

Question 14. Treatment given to Entamoeba cyst carriers is:

1. Metronidazole
2. Diloxanidefuroate
3. Paromomycin
4. Nitzoxzanide

Answer. (3) (Paromomycin)

• Luminal agents (paromomycin or iodoquinol) are given to asymptomatic cyst passers to ensure eradication of the infection Paromomycin is the preferred agent.
• Asymptomatic individuals infected with E. histolytica should be treated because of the risks of developing amoebic colitis or amoebic liver abscess and of transmitting the infection to other
• Amoebic dysentery or Amoebic Liver Abscess: DOC is Tinidazole and Metronidazole.

Question 15. The largest protozoan is:

1. E. Histolytica
2. Balantidium coli
3. E. Coli
4. Plasmodium

Answer. (2) (Balantidium coli)

• Balantidium coli, the largest protozoan and the only ciliated parasite of humans were.
• Balantidium coli is a large ciliated protozoal parasite that can produce a spectrum of large intestinal disease analogous to amebiasis.
• Trophozoite of B.coli: Oval shaped 30–300 µm in length and 30–100 µm in breadth.

Question 16. A patient presents with lower gastrointestinal Sigmoidoscopy shows ulcer in the sigmoid biopsy from this area shows flask-shaped ulcers. Which of the following is the most appropriate treatment?

1. Intravenous ceftriaxone
2. Intravenous metronidazole
3. Intravenous steroids and sulfasalazine
4. Hydrocortisone enemas

Answer. (2) (Intravenous steroids and sulfasalazine)

• The given history of lower GIT bleed with ‘classical flask-shaped ulcers in Sigmoid colon’ suggests intestinal Amebiasis caused by E. histolytica.
• The localized amoebic ulcers are commonly present in the Ileocaecal region and less commonly in sigmoid-rectal region.
• Treatment of intestinal Amoebiasis: Tinidazole, 2 g/d PO with food for 3 days
• Metronidazole (750 mg tid PO or IV), for 5–10 days
• Tinidazole appears to be better tolerated and slightly more effective than metronidazole for amoebic colitis and amoebic liver abscess.

Question 17. Which is not causing neurodegeneration?

1. Balamuthia
2. Iodamoeba
3. Naegleria
4. Entamoeba

Answer. (2) (Iodamoeba)

Question 18. Naegleria fowleri is found in:

1. Sulfur springs
2. Warm fresh water
3. Cold fresh water
4. Sea water

Answer. (2) (Warm freshwater)

• Naegleria is a free-living amoeba, typically found in warm freshwater, such as ponds, lakes, rivers, and hot springs. It is also found in soil, near warm water discharges of industrial plants, and swimming pools.

Question 19. Most common organism causing keratitis infection in soft contact lens users is:

1. Naegleria
2. Acanthamoeba
3. Gonococcus
4. Staphylococcus aureus

Answer. (2) (Acanthamoeba)

• Acanthamoeba causes keratitis in soft contact lens users.
• Protozoan Parasites Helminths

Question 20. Acute meningoencephalitis is caused by:

1. Acanthamoeba
2. Naegleria
3. Meningococcus
4. Balmuthia

Answer. (2) (Naegleria)

• Naegleria fowleri: Agent of Primary Amoebic meningoencephalitis
• Acanthamoeba: Agent of granulomatous amoebic encephalitis.

Question 21. A patient following the use of contact lenses, developed corneal ulcers and symptoms of conjunctivitis. Saline mount preparation of corneal scrapping shows polygonal cyst.What should be the probable diagnosis?

1. Acanthamoeba
2. Naegleria
3. Entamoeba
4. Giardia

Answer. (1) (Acanthamoeba)

• Acanthamoeba keratitis is associated with corneal injuries complicated by exposure to water or soil and with the wearing of contact lenses.
• Acanthamoeba keratitis:
  •  Risk factors:
    • Extended wear of lens
    • Breaches in hygiene and disinfection procedures
    • Swimming with contact lenses in place
    • Use of homemade saline solutions contaminated with Acanthamoeba.

Question 22. Acute Primary Amoebic meningoencephalitis true is:

1. Meningitis caused by Acanthamoeba species is acute
2. Diagnosis is by demonstration of trophozoite in CSF
3. Caused by fecal-oral transmission
4. More common in tropical culture

Answer. (2) (Diagnosis is by demonstration of trophozoite in CSF)

Primary Amoebic meningoencephalitis

• Caused by Naegleria fowleri, which is acute and suppurative (Granulomatous amoebic encephalitis caused by Acanthamoeba species is chronic in nature)
• Diagnosis is by demonstration of trophozoite in CSF (GAE is diagnosed by demonstration of both Acanthamoeba trophozoite and cyst in CSF)
• Transmitted by: Respiratory mode (Acanthamoeba by Respiratory or rarely through skin penetration)
• More common in temperate climates (Acanthamoeba is common in the tropics).

Question 23. A 30-year-old patient presented with features of acute meningoencephalitis in the casualty. His CSF on wet mount microscopy revealed motile unicellular microorganisms. The most likely organism is:

1. Naegleria fowleri
2. Acanthamoeba castellani
3. Entamoeba histolytica
4. Trypanosoma cruzi

Answer. (1) (Naegleria fowleri)

• Provided history of acute meningoencephalitis with a demonstration of motile trophozoites in CSF wet mount suggests the diagnosis of N.fowleri. (Already explained)
• Even though Acanthamoeba also causes meningoencephalitis, it is not acute and it occurs mainly in immunocompromised hosts.

Question 24. Parasitic Encephalitis is caused by:

1. Naegleria
2. Acanthamoeba
3. Balamuthia
4. Gnathostoma

Answer. (1, 2, 3, 4) (Naegleria, Acanthamoeba, Balamuthia, and Gnathostoma)

1. Parasites causing CNS infections
2. Trypanosoma brucei and T. Cruzi
3. Toxoplasma gondii

Question 25. The girl visits her friend’s village, develops nasal discharge, and meningitis, and dies in 5 days.

1. The organism responsible is:
2. Naegleria fowleri
3. Acanthamoeba
4. Toxoplasma
5. P. falciparum

Answer. (1) (Naegleria fowleri)

History of sudden onset of nasal discharge, meningitis, and death in 5 days: Indicates primary amoebic meningoencephalitis (PAM). The agent of PAM is Naegleria fowleri.