Parasitology Practice Questions

Q: Which organism causes biliary duct obstruction?

Clonorchis sinensis. **Explanation:** **Clonorchis sinensis** (the Chinese Liver Fluke) is the correct answer because its primary habitat in the human body is the **biliary passages**. After ingestion of undercooked freshwater fish containing metacercariae, the larvae migrate to the distal bile ducts. Chronic infection leads to mechanical obstruction, inflammatory hyperplasia of the biliary epithelium, and periductal fibrosis. This can manifest clinically as biliary colic, jaundice, and cholangitis. **Analysis of Incorrect Options:** * **Ankylostoma duodenale (Hookworm):** Resides in the small intestine (jejunum) and attaches to the mucosa to suck blood, primarily causing iron-deficiency anemia, not biliary obstruction. * **Strongyloides stercoralis:** Primarily inhabits the mucosal glands of the duodenum and upper jejunum. It is known for its autoinfection cycle and hyperinfection syndrome in immunocompromised patients. * **Enterobius vermicularis (Pinworm):** Lives in the cecum and appendix. Its most common clinical presentation is perianal pruritus (itching) due to nocturnal egg deposition. **High-Yield Clinical Pearls for NEET-PG:** * **Carcinogenesis:** Chronic *Clonorchis sinensis* infection is a major risk factor for **Cholangiocarcinoma** (bile duct cancer). It is classified as a Group 1 carcinogen by the IARC. * **Intermediate Hosts:** 1st host: Snail (Parafossarulus); 2nd host: Cyprinidae family fish. * **Diagnosis:** Identification of characteristic "operculated eggs with a small knob" in stool or biliary aspirate. * **Treatment:** Praziquantel is the drug of choice. * **Other Biliary Flukes:** *Opisthorchis viverrini* and *Fasciola hepatica* can also cause similar biliary pathology.

Q: Nocturnal pruritus ani is characteristic of which of the following?

Enterobius. **Explanation:** **Enterobius vermicularis** (Pinworm or Seatworm) is the correct answer because of its unique life cycle. Unlike most intestinal nematodes, the gravid female Enterobius migrates out of the anus, typically at night (**nocturnal migration**), to deposit eggs on the perianal and perineal skin. The movement of the worm and the sticky substance used to adhere the eggs cause intense local irritation, leading to **nocturnal pruritus ani** (perianal itching). This often results in sleep disturbance and irritability in children. **Analysis of Incorrect Options:** * **Ascaris lumbricoides:** Primarily causes Loeffler’s syndrome (pulmonary phase) and intestinal obstruction. It does not migrate to the perianal region. * **Trichuris trichiura (Whipworm):** Associated with mucosal damage in the large intestine. Heavy infections typically lead to chronic diarrhea and **rectal prolapse**, but not perianal itching. * **Ancylostoma duodenale (Hookworm):** Known for causing iron deficiency anemia due to blood-sucking and "ground itch" at the site of larval skin penetration (usually the feet). **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The investigation of choice is the **NIH Swab** or **Scotch Tape Test** (Cellophane tape test) performed early in the morning before bathing. Eggs are rarely found in routine stool samples. * **Morphology:** Eggs are characteristic **Planoconvex** (D-shaped). * **Transmission:** Autoinfection is common due to the finger-to-mouth transfer of eggs following scratching (fecal-oral). * **Treatment:** **Albendazole** or Mebendazole is used. It is crucial to treat the **entire family** simultaneously to prevent reinfection.

Q: Cysticercosis is caused by:

Taenia solium. **Explanation:** The correct answer is **Taenia solium**. **1. Why Taenia solium is correct:** Cysticercosis occurs when a human becomes the **accidental intermediate host** by ingesting the **eggs** of *Taenia solium* (pork tapeworm) via contaminated food or water (fecal-oral route) or through autoinfection. Once ingested, the eggs hatch into oncospheres, penetrate the intestinal wall, and disseminate to tissues (brain, muscles, eyes) where they develop into larvae called **Cysticercus cellulosae**. *Note:* Ingesting the *larvae* in undercooked pork causes intestinal Taeniasis, but ingesting the *eggs* causes Cysticercosis. **2. Why other options are incorrect:** * **Taenia saginata (Beef tapeworm):** Humans are the definitive hosts and only develop intestinal infections. *T. saginata* does **not** cause cysticercosis in humans because the eggs are not infectious to us; the intermediate stage occurs only in cattle. * **Echinococcus:** This genus (e.g., *E. granulosus*) causes **Hydatid disease** (Cystic Echinococcosis), characterized by slow-growing unilocular cysts, typically in the liver or lungs. **NEET-PG High-Yield Pearls:** * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in developing countries. * **Diagnosis:** MRI/CT shows "starry sky" appearance (multiple calcified cysts) or a "scolex within a cyst" (pathognomonic). * **Drug of Choice:** Albendazole is preferred over Praziquantel for NCC as it has better CNS penetration. * **Morphology:** *T. solium* has a rostellum with hooks (armed), whereas *T. saginata* does not (unarmed).

Q: All of the following organisms cause malabsorption, EXCEPT?

Ancylostoma duodenale. **Explanation:** The core concept tested here is the distinction between parasites that cause **malabsorption** (by damaging the intestinal mucosa or creating a physical barrier) and those that cause **iron-deficiency anemia** (by blood loss). **Why Ancylostoma duodenale is the correct answer:** *Ancylostoma duodenale* (Hookworm) primarily resides in the small intestine, where it attaches to the mucosa using its teeth/cutting plates to suck blood. Its primary clinical manifestation is **Iron Deficiency Anemia (IDA)** and protein loss (hypoalbuminemia) due to chronic hemorrhage. It does not typically cause generalized malabsorption of fats, carbohydrates, or vitamins. **Why the other options are incorrect:** * **Giardia lamblia:** The classic cause of malabsorption. It coats the duodenal mucosa (blunting villi), leading to "steatorrhea" (foul-smelling, fatty stools) and deficiency of fat-soluble vitamins (A, D, E, K). * **Strongyloides stercoralis:** In heavy infections, these larvae penetrate the intestinal wall, causing significant mucosal inflammation, villous atrophy, and a malabsorption syndrome similar to Celiac disease. * **Capillaria philippinensis:** This parasite causes "intestinal capillariasis," characterized by severe mucosal damage leading to massive protein-losing enteropathy and electrolyte imbalance (malabsorption). **NEET-PG High-Yield Pearls:** 1. **Hookworm Fact:** *A. duodenale* sucks more blood (0.15–0.2 ml/day) than *Necator americanus* (0.03 ml/day). 2. **Malabsorption List:** Other parasites causing malabsorption include *Cryptosporidium parvum*, *Isospora belli*, and *Microsporidia* (especially in HIV patients). 3. **D-Xylose Test:** Often used to differentiate mucosal malabsorption (like Giardiasis) from pancreatic insufficiency.

Q: Which of the following is NOT a feature of Entamoeba histolytica?

Cartwheel appearance on CT. The correct answer is **D. Cartwheel appearance on CT**. ### **Explanation** The **Cartwheel appearance** on imaging (CT/Ultrasound) is a classic radiological sign of a **Hydatid cyst** (caused by *Echinococcus granulosus*), not *Entamoeba histolytica* [2], [3]. This appearance occurs due to the presence of multiple daughter cysts and internal septations within the mother cyst [3]. *Entamoeba histolytica* typically presents as an **Amoebic Liver Abscess (ALA)**. On CT, it appears as a well-defined, low-attenuation lesion, often with a peripheral enhancing rim, but it lacks the internal daughter cysts seen in Hydatid disease. ### **Why other options are features of E. histolytica:** * **A. Bloody diarrhea:** *E. histolytica* causes intestinal amoebiasis by invading the colonic mucosa, leading to characteristic **flask-shaped ulcers**. This results in "amoebic dysentery," characterized by blood and mucus in the stool [1]. * **B. Amoeboma in the right iliac fossa:** An amoeboma is a chronic inflammatory pseudotumor (granuloma) that forms in the colon, most commonly in the **cecum** or ascending colon [1]. It can present as a palpable mass in the right iliac fossa, mimicking carcinoma or appendicular mass [1]. * **C. Hepatomegaly:** Extra-intestinal amoebiasis most commonly affects the liver [1]. Patients with an Amoebic Liver Abscess typically present with fever, right upper quadrant pain, and **tender hepatomegaly**. ### **High-Yield NEET-PG Pearls:** * **Trophozoites:** The diagnostic stage in stool; they may contain **ingested RBCs** (erythrophagocytosis). * **Anchovy Sauce Pus:** The classic description of the aspirated material from an amoebic liver abscess (sterile, odorless, chocolate-brown) [1]. * **Treatment:** Metronidazole or Tinidazole (to kill trophozoites) followed by a luminal agent like Paromomycin or Diloxanide furoate (to clear cysts).

Q: What is the commonest helminthic infection in AIDS patients?

Strongyloides stercoralis. **Explanation:** **Strongyloides stercoralis** is the correct answer because of its unique ability to cause **autoinfection**. In immunocompetent individuals, the infection is usually chronic and low-grade. However, in immunocompromised states—particularly in AIDS patients or those on high-dose corticosteroids—the normal immune response (Th2 and eosinophils) that keeps the larval population in check is impaired. This leads to **Hyperinfection Syndrome**, where larvae rapidly multiply and disseminate to extra-intestinal organs (lungs, liver, CNS), making it the most clinically significant and common opportunistic helminthic infection in this population. **Analysis of Incorrect Options:** * **A. Trichuris trichiura (Whipworm):** While common in tropical areas, its prevalence does not specifically increase in AIDS patients as it does not have an internal autoinfection cycle. * **C. Enterobius vermicularis (Pinworm):** This is the most common helminthic infection in children globally, but its lifecycle is limited to the perianal area and large intestine; it does not cause systemic opportunistic disease in HIV. * **D. Necator americanus (Hookworm):** Though it causes significant morbidity (anemia), it requires a soil phase to complete its lifecycle and cannot replicate within the human host to cause hyperinfection. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Choice:** The **Baermann technique** or agar plate culture is preferred over routine stool microscopy for *Strongyloides*. * **Drug of Choice:** **Ivermectin** is the first-line treatment (superior to Albendazole). * **Complication:** Disseminated strongyloidiasis often presents with **Gram-negative sepsis** (e.g., *E. coli* meningitis) because the larvae carry enteric bacteria as they migrate through the intestinal wall into the bloodstream.

Q: Which of the following parasitic infestations can lead to malabsorption syndrome?

Giardiasis. **Explanation:** **Giardiasis** is the correct answer because *Giardia lamblia* primarily colonizes the **duodenum and upper jejunum**. The trophozoites attach to the intestinal mucosa using a ventral sucking disc, causing "carpeting" of the surface. This leads to: 1. **Blunting of villi** and inflammation of the mucosa. 2. **Malabsorption of fats** (steatorrhea) and fat-soluble vitamins (A, D, E, K). 3. **Disaccharidase deficiency** (especially lactase), leading to secondary lactose intolerance. The classic clinical presentation is foul-smelling, frothy, greasy stools that float in water, without blood or mucus. **Why the other options are incorrect:** * **Amoebiasis (*Entamoeba histolytica*):** Primarily involves the **colon**. It causes "flask-shaped ulcers" and invasive diarrhea (amoebic dysentery) with blood and mucus, rather than malabsorption. * **Ascariasis (*Ascaris lumbricoides*):** While heavy infestations can cause nutritional deficiency or intestinal obstruction, they do not typically cause a formal malabsorption syndrome. * **Hookworm (*Ancylostoma duodenale*):** The hallmark of hookworm infestation is **Iron Deficiency Anemia** due to chronic blood loss from the intestinal wall, not generalized malabsorption. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Metronidazole or Tinidazole. * **Diagnosis:** Stool microscopy (cysts/trophozoites) or the **Entero-test (String test)**. * **Risk Group:** Common in children, travelers, and individuals with **IgA deficiency**. * **Other parasites causing malabsorption:** *Strongyloides stercoralis*, *Cryptosporidium parvum*, and *Isospora belli*.

Q: Which of the following organisms is characterized by the presence of both cyst and trophozoite stages in stool samples?

Toxoplasma. **Explanation:** The question focuses on the life cycle stages of common pathogens. **Toxoplasma gondii** is an obligate intracellular protozoan. While its definitive hosts are felids (cats), humans serve as intermediate hosts. In the context of human infection and diagnostic samples, *Toxoplasma* can be identified in various forms: **oocysts** (shed in cat feces), **tachyzoites** (active, rapidly multiplying form), and **bradyzoites** (latent form in tissue cysts). While stool examination is primarily used to detect oocysts in cats, the presence of cystic and vegetative (trophozoite-like) stages is a hallmark of its complex life cycle compared to the other options provided. **Analysis of Incorrect Options:** * **A. Mycoplasma:** These are the smallest free-living bacteria. They lack a cell wall and do not have cyst or trophozoite stages; they replicate via binary fission. * **C. Leptospira:** These are thin, coiled spirochetes. They are typically diagnosed via blood, CSF, or urine cultures/microscopy (dark-field) and do not form cysts. * **D. Treponema:** Another genus of spirochetes (e.g., *T. pallidum* causing Syphilis). They are highly motile bacteria but do not possess a protozoan-style cyst/trophozoite life cycle. **NEET-PG High-Yield Pearls:** * **Toxoplasmosis Triad (Congenital):** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Diagnosis:** Sabin-Feldman Dye Test is the gold standard (detects antibodies). * **Morphology:** Tachyzoites are characteristically crescent-shaped. * **Transmission:** Ingestion of undercooked meat containing tissue cysts or food/water contaminated with oocysts from cat feces.

Question 1

A patient complains of diarrhea. Stool examination shows ova. Which of the following cannot be the cause?

Accepted Answer

Opisthorchis viverni

Answer

Cryptosporidium

Answer

Isospora

Answer

E. histolytica

Question 2

Which organism causes biliary duct obstruction?

Accepted Answer

Clonorchis sinensis

Answer

Ankylostoma duodenale

Answer

Strongyloides stercales

Answer

Enterobius vermicularis

Question 3

Nocturnal pruritus ani is characteristic of which of the following?

Accepted Answer

Enterobius

Answer

Ascaris

Answer

Trichuris

Answer

Ancylostoma

Question 4

Cysticercosis is caused by:

Accepted Answer

Taenia solium

Answer

Taenia saginata

Answer

Echinococcus

Answer

None of the above

Question 5

All of the following are true about Toxoplasma infection EXCEPT:

Accepted Answer

Toxoplasmosis is usually symptomatic in immunocompetent persons

Answer

May occur due to ingestion of oocyst from cat's faeces

Answer

May spread by organ transplantation

Answer

Infection is severe and progressive in immunocompromised hosts

Question 6

All of the following organisms cause malabsorption, EXCEPT?

Accepted Answer

Ancylostoma duodenale

Answer

Giardiasis

Answer

Strongyloides stercoralis

Answer

Capillaria philippinensis

Question 7

Which of the following is NOT a feature of Entamoeba histolytica?

Accepted Answer

Cartwheel appearance on CT

Answer

Bloody diarrhea

Answer

Amoeboma in the right iliac fossa

Answer

Hepatomegaly

Question 8

What is the commonest helminthic infection in AIDS patients?

Accepted Answer

Strongyloides stercoralis

Answer

Trichuris trichura

Answer

Enterobius vermicularis

Answer

Necator americanus

Question 9

Which of the following parasitic infestations can lead to malabsorption syndrome?

Accepted Answer

Giardiasis

Answer

Amoebiasis

Answer

Ascariasis

Answer

Hookworm infestation

Question 10

Which of the following organisms is characterized by the presence of both cyst and trophozoite stages in stool samples?

Accepted Answer

Toxoplasma

Answer

Mycoplasma

Answer

Leptospira

Answer

Treponema

Parasitology — MCQs

Parasitology — MCQs

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