Intestinal Protozoa — MCQs
A 30-year-old man with HIV presents with chronic diarrhea. Stool examination reveals small, spherical, acid-fast oocysts. What is the causative agent?
Amoebic liver abscess can be diagnosed by demonstrating-
Which of the following is the MOST characteristic clinical feature of Giardiasis?
A 4 year old child presents with acute watery diarrhea and abdominal cramps. Stool microscopy reveals trophozoites with falling leaf motility. What is the etiological agent?
A 6-year-old child is brought with high fever with rigors for 5 days with pain in right hypochondrium. On examination, the patient is anicteric and tenderness is noted in right upper quadrant. What is the best investigation for this case?
A known HIV patient on anti-retroviral therapy presented with diarrhea of six months duration. Stool microscopy showed 10-30 micrometer cysts, Kinyoun stain was positive. What is the most likely diagnosis?
A 15-year-old boy returned from a vacation to his relatives' village. He developed a severe headache and purulent nasal discharge and was diagnosed with primary amebic meningoencephalitis (PAM). He died 5 days later. Which is the most likely etiological agent?
Flask-shaped ulcers in the intestine are caused by which of the following?
Cercariae are the infective form of which of the following parasites?
Largest intestinal protozoan is?
Intestinal Protozoa Indian Medical PG Practice Questions and MCQs
Question 1: A 30-year-old man with HIV presents with chronic diarrhea. Stool examination reveals small, spherical, acid-fast oocysts. What is the causative agent?
- A. Entamoeba histolytica
- B. Cryptosporidium parvum (Correct Answer)
- C. Isospora belli
- D. Giardia lamblia
Explanation: ***Cryptosporidium parvum*** - This is the **most common cause** of chronic, watery diarrhea in immunocompromised individuals, particularly those with **HIV/AIDS**. - Its oocysts are **acid-fast**, small (4-6 μm), and typically **spherical**, readily identified in stool samples using modified acid-fast staining methods. - Causes self-limiting diarrhea in immunocompetent hosts but severe, persistent diarrhea in AIDS patients with CD4 count <200. *Entamoeba histolytica* - Causes **amoebic dysentery** characterized by bloody diarrhea, abdominal pain, and liver abscesses, but its cysts are **not acid-fast**. - Identification involves finding **trophozoites with ingested red blood cells** or cysts in stool, not acid-fast oocysts. *Isospora belli (Cystoisospora belli)* - Also causes chronic diarrhea in HIV patients and produces acid-fast oocysts, but its oocysts are **ellipsoidal, much larger (20-30 μm)**, and contain two sporoblasts. - While also acid-fast, its morphology in stool microscopy differs significantly from the smaller, round oocysts characteristic of *Cryptosporidium*. *Giardia lamblia* - Causes **giardiasis**, characterized by non-bloody, foul-smelling diarrhea, steatorrhea, and malabsorption. - Its cysts and trophozoites are identified in stool, but they are **not acid-fast** and have distinct pear-shaped trophozoites and oval cysts with nuclei.
Question 2: Amoebic liver abscess can be diagnosed by demonstrating-
- A. Trophozoites in the pus (Correct Answer)
- B. Trophozoites in the feces
- C. Cysts in the pus
- D. Cysts in the liver
Explanation: ***Trophozoites in the pus*** - **Amoebic liver abscesses** are caused by the invasive **trophozoite stage** of *Entamoeba histolytica*. - Demonstrating **trophozoites** in the characteristic **'anchovy paste' pus** aspirated from the abscess cavity is diagnostic. *Cysts in the pus* - **Cysts** are the **infective stage** of *Entamoeba histolytica* and are typically found in the **feces**, not in an abscess. - Cysts are responsible for transmission and survival outside the host, but they do not cause invasive disease. *Cysts in the liver* - The disease in the liver is caused by **trophozoites**, which invade the intestinal wall and then spread to the liver. - **Cysts** are never found within the liver parenchyma or abscesses. *Trophozoites in the feces* - While **trophozoites** can be found in the feces during acute amoebic dysentery, their presence alone does not confirm a liver abscess. - Furthermore, **trophozoites** are fragile and often difficult to detect in stool samples, especially once the stool has cooled.
Question 3: Which of the following is the MOST characteristic clinical feature of Giardiasis?
- A. Diarrhea with foul-smelling stools (Correct Answer)
- B. Presence of Giardia cysts in stool
- C. Abdominal cramps and bloating
- D. Nausea and vomiting
Explanation: ***Diarrhea with foul-smelling stools*** - This is a hallmark symptom of Giardiasis [1], resulting from **malabsorption of fats** due to parasite adherence to the intestinal lining. - The malabsorption leads to **steatorrhea**, characterized by greasy, malodorous, and often floating stools. *Presence of Giardia cysts in stool* - While essential for **diagnosis**, the presence of cysts in stool is a **laboratory finding**, not a clinical feature experienced by the patient. - Clinical features refer to the **symptoms and signs** a patient presents with [1], which are often what prompt diagnostic testing. *Abdominal cramps and bloating* - These are **common symptoms** of Giardiasis, but they are often present in various gastrointestinal disturbances and are **less specific** than foul-smelling diarrhea. - They also can be caused by gas production and intestinal irritation, which frequently accompany many forms of infectious diarrhea. *Nausea and vomiting* - Nausea and vomiting can occur in Giardiasis, but they are **less consistent** and characteristic than the distinctive diarrhea pattern. - These symptoms are **widespread in many gastrointestinal illnesses** and do not specifically point to Giardiasis more than other conditions.
Question 4: A 4 year old child presents with acute watery diarrhea and abdominal cramps. Stool microscopy reveals trophozoites with falling leaf motility. What is the etiological agent?
- A. Giardia lamblia (Correct Answer)
- B. Trichomonas tenax
- C. Balantidium coli
- D. Entamoeba histolytica
Explanation: **Giardia lamblia** - The presence of **trophozoites** with characteristic **falling leaf motility** in stool microscopy is pathognomonic for **Giardia lamblia** infection. - **Giardiasis** commonly causes **acute watery diarrhea** and **abdominal cramps** in children, often acquired through contaminated water or food. *Entamoeba histolytica* - **Entamoeba histolytica** causes **amoebic dysentery**, characterized by bloody diarrhea, unlike the watery diarrhea described. - Its trophozoites exhibit **directional motility** with pseudopods and may contain ingested red blood cells, not falling leaf motility. *Trichomonas tenax* - **Trichomonas tenax** is found in the **oral cavity** and is not associated with intestinal infections or diarrhea. - Its typical habitat and clinical presentation are entirely different from the symptoms described. *Balantidium coli* - **Balantidium coli** is a large, ciliated protozoan whose trophozoites have a **distinctive kidney-shaped macronucleus** and rotary motility with cilia. - It causes **balantidiasis**, which can range from asymptomatic to dysentery, but its trophozoite morphology and motility are distinct from falling leaf.
Question 5: A 6-year-old child is brought with high fever with rigors for 5 days with pain in right hypochondrium. On examination, the patient is anicteric and tenderness is noted in right upper quadrant. What is the best investigation for this case?
- A. SGOT/LFT
- B. CECT
- C. Serology
- D. USG (Correct Answer)
Explanation: ***USG*** - A **ultrasound** is the preferred initial investigation, especially in children, for evaluating abdominal pain in the **right hypochondrium** with fever. - It can effectively identify common causes like **cholecystitis**, **hepatitis**, or **liver abscess**, which fit the clinical presentation. *SGOT/LFT* - **Liver function tests (LFTs)** like SGOT/AST and SGPT/ALT provide information about liver inflammation or damage but do not help localize the pathology. - They are useful for assessing liver function but are not the primary diagnostic tool to identify the cause of the pain or fever. *CECT* - **Contrast-enhanced computed tomography (CECT)** is a more advanced imaging technique, often used after initial screening or when ultrasound findings are inconclusive. - It involves radiation exposure and contrast risks, making it less suitable as a first-line investigation for a child with these symptoms. *Serology* - **Serological tests** detect antibodies or antigens related to specific infections (e.g., viral hepatitis) but do not provide immediate anatomical information. - While they can confirm an infectious cause, they cannot identify the source of the pain or rule out other non-infectious pathologies immediately.
Question 6: A known HIV patient on anti-retroviral therapy presented with diarrhea of six months duration. Stool microscopy showed 10-30 micrometer cysts, Kinyoun stain was positive. What is the most likely diagnosis?
- A. Balantidium coli
- B. Cryptosporidium
- C. Cystoisospora (Correct Answer)
- D. Strongyloides
Explanation: ***Cystoisospora*** - **Cystoisospora belli** is a common cause of chronic diarrhea in **HIV-infected patients** and presents with oocysts typically measuring **20-30 µm** (the described 10-30 micrometer range encompasses the typical size). - The **Kinyoun acid-fast stain** is characteristically positive for *Cystoisospora* oocysts, which is the key diagnostic feature supporting this diagnosis. - This organism is particularly important in **immunocompromised patients** on ART who present with chronic diarrhea. *Balantidium coli* - **Balantidium coli** is a large ciliate, and its cysts are significantly larger (typically **40-60 µm**) than those described in the patient's stool. - While it can cause diarrhea in immunocompromised individuals, it is **not acid-fast** and therefore would not be positive with the Kinyoun stain. *Cryptosporidium* - **Cryptosporidium** is another common cause of chronic diarrhea in HIV patients, and its oocysts are **acid-fast positive** with the Kinyoun stain. - However, **Cryptosporidium** oocysts are much smaller, typically **4-6 µm**, which is inconsistent with the 10-30 micrometer cysts observed in this case. *Strongyloides* - **Strongyloides stercoralis** is a nematode that can cause chronic diarrhea and hyperinfection in immunocompromised patients, but it primarily produces **larvae** (rhabditiform and filariform) in stool, not cysts. - Its diagnostic forms are **not acid-fast**, and its morphology in stool microscopy is distinctly different from the described cysts.
Question 7: A 15-year-old boy returned from a vacation to his relatives' village. He developed a severe headache and purulent nasal discharge and was diagnosed with primary amebic meningoencephalitis (PAM). He died 5 days later. Which is the most likely etiological agent?
- A. Plasmodium falciparum
- B. Entamoeba histolytica
- C. Naegleria fowleri (Correct Answer)
- D. Toxoplasma
Explanation: ***Naegleria fowleri*** - This free-living amoeba is the causative agent of **Primary Amebic Meningoencephalitis (PAM)**, a rapidly fatal infection acquired through nasal exposure to contaminated warm freshwater. - The rapid progression from symptom onset (headache, purulent nasal discharge) to death within 5 days is characteristic of PAM caused by **_Naegleria fowleri_**. *Plasmodium falciparum* - This parasite causes **falciparum malaria**, which can lead to cerebral malaria, but its presentation involves cyclic fevers, chills, and typically a longer disease course and different diagnostic markers than PAM. - While it affects the brain, it does not cause purulent nasal discharge or the rapid, fulminant meningoencephalitis seen in PAM. *Entamoeba histolytica* - This amoeba causes **amebic dysentery** and, in rare cases, extraintestinal amebiasis like liver abscesses; it does not typically cause PAM. - Central nervous system involvement by _Entamoeba histolytica_ is usually secondary to systemic spread and manifests as abscesses, not a fulminant meningoencephalitis acquired via nasal passages. *Toxoplasma* - _Toxoplasma gondii_ causes toxoplasmosis, which can lead to toxoplasmic encephalitis, especially in immunocompromised individuals. - _Toxoplasma_ infection typically has a slower onset, different risk factors (e.g., raw meat, cat feces), and does not present with a rapid, purulent meningoencephalitis following swimming exposure.
Question 8: Flask-shaped ulcers in the intestine are caused by which of the following?
- A. TB
- B. Giardia
- C. Entamoeba histolytica (Correct Answer)
- D. Typhoid
Explanation: ***Entamoeba histolytica*** - *Entamoeba histolytica* is a protozoan that causes **amoebiasis**, which is characterized by **flask-shaped (bottle-shaped) ulcers** in the colon - this is the **pathognomonic feature** of intestinal amoebiasis. - The trophozoites invade the intestinal mucosa and submucosa, creating a **narrow neck at the mucosal surface** and a **wider base in the submucosa**, giving them their unique flask-like appearance. - These ulcers are most commonly found in the **cecum and ascending colon**. *TB* - Intestinal tuberculosis typically causes **transverse ulcers** (perpendicular to the bowel axis) due to lymphatic spread and caseous necrosis, often in the ileocecal region. - These ulcers are usually associated with **granulomas** and acid-fast bacilli, which are histologically distinct from flask-shaped ulcers. *Giardia* - *Giardia lamblia* (or *intestinalis*) is a flagellate that causes **giardiasis**, primarily adhering to the small intestinal villi and causing malabsorption and diarrhea. - It is **non-invasive** and does not penetrate the intestinal wall or cause ulcer formation; its pathology is mainly due to **mucosal inflammation** and villous blunting. *Typhoid* - Typhoid fever, caused by *Salmonella Typhi*, commonly leads to **longitudinal ulcers** (parallel to the bowel axis) in the **Peyer's patches** of the ileum due to bacterial invasion and necrosis of lymphoid tissue. - These ulcers may perforate but do not present with the flask-shaped morphology characteristic of amoebiasis.
Question 9: Cercariae are the infective form of which of the following parasites?
- A. Schistosoma hematobium (Correct Answer)
- B. Paragonimus westermani
- C. Fasciola hepatica
- D. Taenia solium
Explanation: ***Schistosoma hematobium*** - **Cercariae** are the motile, free-swimming larval stage of **Schistosoma** species, including *S. hematobium* - They **actively penetrate human skin** to initiate infection, making cercariae the infective form for humans *Paragonimus westermani* - The infective form for humans is **metacercariae**, which are ingested by consuming insufficiently cooked **crabs or crayfish** - Cercariae develop into metacercariae in secondary intermediate hosts (crustaceans) *Fasciola hepatica* - Humans are infected by ingesting **metacercariae** present on aquatic vegetation, such as **watercress** - Cercariae encyst on plants to form metacercariae, not directly infective *Taenia solium* - The infective forms are **cysticerci** in undercooked pork (for adult tapeworm) or **embryonated eggs** (causing cysticercosis) - This cestode has a different life cycle and does **not** involve cercariae
Question 10: Largest intestinal protozoan is?
- A. E. coli
- B. Balantidium coli (Correct Answer)
- C. Giardia
- D. T. gondii
Explanation: ***Balantidium coli*** - *Balantidium coli* is the **largest protozoan parasite** known to infect humans, specifically found in the intestines. - It causes **balantidiasis**, an intestinal infection, and is notable for its ciliated trophozoite stage. *E. coli* - *E. coli* is a **bacterium**, not a protozoan. - While it is a common inhabitant of the intestines, it is significantly smaller than parasitic protozoa. *Giardia* - *Giardia lamblia* (or *intestinalis*) is a **flagellate protozoan** that causes giardiasis. - Though an intestinal parasite, it is considerably smaller than *Balantidium coli*. *T. gondii* - *Toxoplasma gondii* is an **intracellular protozoan parasite** known for causing toxoplasmosis. - It is much smaller than *Balantidium coli* and primarily infects cells, not existing as a large free-living form in the intestine.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free