Parasitology Practice Questions

Q: Which of the following is associated with bile duct carcinoma?

Both Clonorchis and Opisthorchis. **Explanation:** The correct answer is **Both Clonorchis and Opisthorchis**. **1. Why the correct answer is right:** *Clonorchis sinensis* (Chinese liver fluke) and *Opisthorchis viverrini/felineus* (Southeast Asian liver flukes) are trematodes that inhabit the distal bile ducts. Chronic infection leads to mechanical irritation, chronic inflammation, and the release of parasite-derived mitogenic factors. This persistent biliary damage induces adenomatous hyperplasia and cellular dysplasia, which are precursors to **Cholangiocarcinoma (Bile duct carcinoma)**. Both parasites are classified as Group 1 carcinogens by the IARC. **2. Why the other options are incorrect:** * **Echinococcus granulosus:** This cestode causes **Hydatid cyst** disease, primarily in the liver. While it can cause complications like cyst rupture or biliary obstruction, it is not associated with malignancy or bile duct carcinoma. * **Clonorchis/Opisthorchis alone:** While both are independent risk factors, selecting only one would be incomplete, as both share the same pathogenic mechanism regarding biliary oncogenesis. **3. NEET-PG High-Yield Clinical Pearls:** * **Infective Stage:** Metacercariae (found in undercooked freshwater fish). * **Intermediate Hosts:** 1st host is a Snail; 2nd host is a Cyprinoid fish. * **Diagnosis:** Stool microscopy for characteristic "operculated eggs" (often described as having a "shouldered" appearance). * **Drug of Choice:** Praziquantel. * **Other Parasite-Cancer Associations:** *Schistosoma haematobium* is strongly associated with **Squamous Cell Carcinoma of the Urinary Bladder**.

Q: Which of the following parasites requires two hosts?

Taenia solium. ### Explanation The correct answer is **Taenia solium** (and notably **Taenia saginata**, though the question structure implies a specific focus on the life cycle requirements). **1. Why Taenia solium is correct:** *Taenia solium* (Pork tapeworm) is a **digenetic parasite**, meaning it requires two hosts to complete its life cycle: * **Definitive Host:** Humans (harbor the adult worm in the small intestine). * **Intermediate Host:** Pigs (harbor the larval stage, *Cysticercus cellulosae*). * **Note on Option C:** *Taenia saginata* also requires two hosts (Humans and Cattle). In many NEET-PG questions, if both are present, the question may be flawed or looking for the one most associated with "Cysticercosis" in humans (where humans can act as accidental intermediate hosts for *T. solium* but not *T. saginata*). **2. Why the other options are incorrect:** * **Entamoeba histolytica:** A monoxenous parasite. It requires only **one host** (Humans). Transmission occurs via the feco-oral route through ingestion of mature quadrinucleate cysts. * **Giardia lamblia:** Also a monoxenous parasite requiring only **one host** (Humans). It exists in two stages: trophozoite and cyst, with the cyst being the infective form. **3. NEET-PG Clinical Pearls:** * **Autoinfection:** *T. solium* is unique because humans can serve as both the definitive and intermediate host. Ingestion of eggs (via contaminated food or autoinfection) leads to **Cysticercosis**, most commonly manifesting as **Neurocysticercosis** (the leading cause of adult-onset seizures in India). * **Infective Stages:** * To get Intestinal Taeniasis: Eat undercooked pork containing *Cysticerci*. * To get Cysticercosis: Ingest *T. solium* eggs. * **High-Yield Distinction:** *T. saginata* has more uterine branches (15–30) than *T. solium* (7–13) and lacks a rostellum/hooks (unarmed).

Q: A pregnant woman on her second pre-natal visit is suspected to have an infection. Her pet cat could act as a reservoir for which of the following conditions?

Toxoplasma gondii. ### Explanation **Correct Answer: A. Toxoplasma gondii** **Reasoning:** *Toxoplasma gondii* is an obligate intracellular protozoan for which members of the **Felidae family (cats)** are the only definitive hosts. Cats shed infective **oocysts** in their feces. Humans (intermediate hosts) typically acquire the infection through the ingestion of soil, water, or vegetables contaminated with these oocysts, or by handling cat litter. In pregnancy, primary infection is critical because the parasite can cross the placenta (**transplacental transmission**), leading to **Congenital Toxoplasmosis**. This can result in the classic triad of chorioretinitis, hydrocephalus, and intracranial calcifications. **Why the other options are incorrect:** * **B. Rabies:** While cats can transmit Rabies, they are considered **accidental hosts** (vectors), not the primary reservoir. The primary reservoirs are wild animals (bats, raccoons) and stray dogs. * **C. Streptocerca infection:** *Mansonella streptocerca* is a filarial nematode transmitted by **biting midges** (*Culicoides*). Humans and primates are the reservoirs, not cats. * **D. Plague:** Caused by *Yersinia pestis*, the primary reservoirs are **wild rodents** (e.g., rats, ground squirrels). Cats can occasionally contract plague and transmit it to humans via respiratory droplets or fleas, but they are not the natural reservoir. **High-Yield NEET-PG Pearls:** * **Definitive Host:** Cat (sexual cycle occurs here). * **Intermediate Host:** Humans/Birds/Rodents (asexual cycle). * **Infective forms:** Oocysts (from cat feces) or Bradyzoites (in undercooked meat). * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard) or IgM/IgG serology. * **Treatment in Pregnancy:** **Spiramycin** is used to prevent transmission to the fetus; if the fetus is already infected, Pyrimethamine and Sulfadiazine are used (after the first trimester).

Q: Visceral larva migrans is associated with which of the following?

Toxocara canis. **Explanation:** **Visceral Larva Migrans (VLM)** is a clinical syndrome caused by the migration of non-human nematode larvae through the internal organs of a human host. **Why Toxocara canis is correct:** *Toxocara canis* (dog roundworm) and *Toxocara cati* (cat roundworm) are the primary causative agents. Humans are accidental hosts who ingest embryonated eggs from soil contaminated with animal feces. Since humans are not the definitive hosts, the larvae cannot complete their life cycle to become adult worms. Instead, they penetrate the intestinal wall and migrate through the **liver, lungs, and eyes**, triggering a robust inflammatory response and marked **peripheral eosinophilia**. **Analysis of Incorrect Options:** * **Strongyloides stercoralis:** Causes **Hyperinfection syndrome** or "Larva currens" (a rapidly moving cutaneous track), but it is a human parasite that completes its life cycle in the human gut. * **Ancylostoma braziliense:** This is the primary cause of **Cutaneous Larva Migrans (CLM)** or "creeping eruption." The larvae penetrate the skin but lack the collagenases to penetrate the basement membrane, remaining confined to the epidermis. * **Visceral leishmaniasis (Kala-azar):** This is caused by a protozoan (*Leishmania donovani*), not a helminth. While it affects internal organs (spleen/liver), it does not involve larval migration. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Presentation:** A young child with a history of pica (eating dirt), hepatomegaly, wheezing, and extreme eosinophilia. * **Ocular Larva Migrans (OLM):** A variant where larvae migrate to the eye, often mimicking a retinoblastoma. * **Diagnosis:** Serology (ELISA) is the preferred method; stool examination is useless because the larvae never mature into egg-laying adults in humans. * **Treatment:** Albendazole or Mebendazole.

Q: Chyluria is due to:

Filaria. **Explanation:** **Chyluria** is the presence of chyle (a milky fluid consisting of lymph and emulsified fats) in the urine. It occurs due to a communication between the intestinal lymphatics and the urinary tract. **Why Filaria is correct:** The most common cause of chyluria worldwide is **Lymphatic Filariasis**, primarily caused by *Wuchereria bancrofti*. The adult worms reside in the lymphatic vessels, leading to chronic inflammation, fibrosis, and eventual **lymphatic obstruction**. This obstruction causes high pressure within the lymphatics (lymphatic hypertension), leading to the rupture of collateral lymphatic vessels into the renal pelvis, ureter, or bladder. The characteristic "milky white" appearance of urine is due to the presence of chylomicrons. **Why other options are incorrect:** * **Carcinoma:** While retroperitoneal tumors can occasionally cause lymphatic obstruction, they are a rare cause of chyluria compared to parasitic infections. * **Tuberculosis:** Renal TB typically presents with "sterile pyuria" (pus cells in urine without bacterial growth on standard media), not chyluria. * **Malaria:** Malaria causes hemolysis, which may lead to **hemoglobinuria** (Blackwater fever in *P. falciparum*), resulting in dark/cola-colored urine, but not milky chyluria. **NEET-PG High-Yield Pearls:** * **Diagnosis:** Chyluria can be confirmed by the **Ether test** (urine clears after adding ether) or by detecting high triglyceride levels in the urine. * **Microfilariae:** Usually show **nocturnal periodicity** (collected between 10 PM – 2 AM). * **Drug of Choice:** Diethylcarbamazine (DEC) is the mainstay for Filariasis, but it does not reverse established structural lymphatic damage. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough and high IgE levels.

Q: What is the most common site of extraintestinal amoebiasis?

Liver. **Explanation:** **Entamoeba histolytica** is primarily an intestinal parasite, but it can spread hematogenously to cause extraintestinal manifestations. **Why Liver is Correct:** The **Liver** is the most common site for extraintestinal amoebiasis. This occurs because trophozoites from the intestinal wall enter the **portal venous system**. Since the portal vein drains directly into the liver, it acts as the first major capillary filter for the parasite. The resulting **Amoebic Liver Abscess (ALA)** typically presents in the right lobe (due to the streamlining of portal blood flow) and is characterized by "anchovy sauce" pus. **Why Other Options are Incorrect:** * **Lungs (Option D):** This is the second most common site. It usually occurs via direct extension from a liver abscess through the diaphragm or, less commonly, through systemic circulation. * **Brain (Option A):** This is a rare, life-threatening complication resulting from hematogenous spread. It typically presents as sudden onset meningoencephalitis. * **Spleen (Option C):** Splenic involvement is extremely rare and usually occurs only in cases of widespread systemic dissemination. **High-Yield Clinical Pearls for NEET-PG:** * **Trophozoite Morphology:** Look for ingested RBCs (Erythrophagocytosis) in the cytoplasm—this is pathognomonic for *E. histolytica*. * **Anchovy Sauce Pus:** The abscess fluid is chocolate-brown, odorless, and sterile (contains no bacteria or trophozoites; trophozoites are found in the abscess wall). * **Treatment:** **Metronidazole** or Tinidazole is the drug of choice for the tissue stage, followed by a luminal amoebicide (e.g., Diloxanide furoate or Paromomycin) to eradicate cysts.

Q: Which tick-borne fever is characterized by an organism that attacks red blood cells?

Babesiosis. **Explanation:** **Babesiosis** is the correct answer because it is a tick-borne zoonosis caused by protozoan parasites of the genus *Babesia* (most commonly *B. microti*). The organism is transmitted by the **Ixodes tick** (the same vector for Lyme disease). Once in the bloodstream, the sporozoites invade **Red Blood Cells (RBCs)**, where they replicate asexually. A hallmark diagnostic feature on a peripheral blood smear is the **"Maltese Cross" appearance** (tetrads of merozoites), which confirms its intra-erythrocytic nature. **Why other options are incorrect:** * **Typhus:** While some forms (like Endemic or Epidemic Typhus) are vector-borne (fleas/lice), **Scrub Typhus** is mite-borne. However, *Rickettsia* species primarily infect **vascular endothelial cells**, not RBCs. * **Dengue:** This is a viral infection transmitted by the **Aedes mosquito**, not ticks. It primarily affects platelets and causes plasma leakage. * **Malaria:** While *Plasmodium* does attack RBCs, it is transmitted by the **Anopheles mosquito**, not ticks. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Ixodes scapularis* (Deer tick). * **Morphology:** Look for "Maltese Cross" or ring forms (often confused with *P. falciparum*, but Babesia lacks hemozoin pigment). * **Clinical Presentation:** Fever, hemolytic anemia, and hemoglobinuria. It can be fatal in asplenic patients. * **Treatment:** Combination of **Atovaquone + Azithromycin** (preferred) or Clindamycin + Quinine.

Q: Which Entamoeba species is morphologically identical to E. histolytica?

E. dispar. ### Explanation **Correct Answer: B. E. dispar** **Why it is correct:** *Entamoeba dispar* is a non-pathogenic commensal that is **morphologically identical** to *E. histolytica* in both its trophozoite and cyst stages. Under a light microscope, they cannot be distinguished by size, nuclear structure, or number of nuclei (both have 1–4 nuclei in the cyst stage). The only definitive way to differentiate them is through **isoenzyme analysis (zymodemes)**, molecular methods (PCR), or by observing ingested RBCs (erythrophagocytosis), which is a feature unique to the pathogenic *E. histolytica*. **Why the other options are incorrect:** * **A. E. coli:** This is a non-pathogenic commensal but is morphologically distinct. The mature cyst has **8 nuclei** (compared to 4 in *E. histolytica*), and the trophozoite has a sluggish motility with a coarse, eccentric karyosome. * **C. E. hartmanni:** Known as the "small race" of *E. histolytica*, it is morphologically similar but significantly **smaller** in size (cysts are <10 µm, whereas *E. histolytica* cysts are 10–15 µm). * **D. E. gingivalis:** This species is found in the oral cavity (gingival pockets). It **does not have a cyst stage** and is the only *Entamoeba* known to ingest White Blood Cells (WBCs). **High-Yield Clinical Pearls for NEET-PG:** * **E. moshkovskii:** Another species morphologically identical to *E. histolytica* and *E. dispar*, usually found in sewage but occasionally in human stools. * **Pathognomonic Feature:** The presence of **ingested RBCs** in a trophozoite is the gold standard for diagnosing invasive amoebiasis caused by *E. histolytica*. * **Treatment Note:** Since *E. dispar* is non-pathogenic, its identification in an asymptomatic patient does not require treatment.

Q: All of the following can cause obstruction of the hepatobiliary system EXCEPT?

Ascaris lumbricoides. **Explanation:** The correct answer is **A. *Ankylostoma duodenale***. The question asks for the organism that does **NOT** typically cause hepatobiliary obstruction. While *Ascaris lumbricoides* is often associated with this condition, the provided key indicates a focus on the primary habitat of these parasites. 1. **Why *Ankylostoma duodenale* is the correct answer:** *Ankylostoma duodenale* (Hookworm) resides primarily in the **upper small intestine (jejunum)**, where it attaches to the mucosa to suck blood. It does not migrate into the biliary tree. Its clinical manifestations are primarily related to iron-deficiency anemia and ground itch, not mechanical obstruction of the liver or bile ducts. 2. **Analysis of other options:** * **B. *Ascaris lumbricoides*:** This is the most common cause of biliary ascariasis. Adult worms are highly motile and can migrate from the duodenum through the Ampulla of Vater into the common bile duct, causing obstructive jaundice, cholangitis, or cholecystitis. * **C. *Clonorchis sinensis* (Chinese Liver Fluke):** These parasites reside directly within the distal bile ducts. Chronic infection leads to mechanical obstruction, inflammatory hyperplasia, and is a major risk factor for **cholangiocarcinoma**. * **D. *Fasciola hepatica* (Sheep Liver Fluke):** After ingestion, the larvae penetrate the liver parenchyma and settle in the bile ducts to mature into adults, causing "liver rot" and biliary obstruction. **High-Yield Clinical Pearls for NEET-PG:** * **Most common helminth causing biliary obstruction:** *Ascaris lumbricoides*. * **Parasite associated with Cholangiocarcinoma:** *Clonorchis sinensis* and *Opisthorchis viverrini*. * **Hookworm (Ankylostoma):** Key association is **Microcytic Hypochromic Anemia** and **Loffler’s Syndrome** (during pulmonary migration). * **Fasciola hepatica:** Acquired by eating contaminated **watercress**.

Question 1

Which of the following is associated with bile duct carcinoma?

Accepted Answer

Both Clonorchis and Opisthorchis

Answer

Clonorchis

Answer

Opisthorchis

Answer

E. granulosus

Question 2

Which of the following parasites requires two hosts?

Accepted Answer

Taenia solium

Answer

Entamoeba histolytica

Answer

Taenia saginata

Answer

Giardia

Question 3

A pregnant woman on her second pre-natal visit is suspected to have an infection. Her pet cat could act as a reservoir for which of the following conditions?

Accepted Answer

Toxoplasma gondii

Answer

Rabies

Answer

Streptocerca infection

Answer

Plague

Question 4

Visceral larva migrans is associated with which of the following?

Accepted Answer

Toxocara canis

Answer

Strongyloides stercoralis

Answer

Ancylostoma braziliense

Answer

Visceral leishmaniasis

Question 5

Chyluria is due to:

Accepted Answer

Filaria

Answer

Carcinoma

Answer

Tuberculosis

Answer

Malaria

Question 6

What is the most common site of extraintestinal amoebiasis?

Accepted Answer

Liver

Answer

Brain

Answer

Spleen

Answer

Lungs

Question 7

Which tick-borne fever is characterized by an organism that attacks red blood cells?

Accepted Answer

Babesiosis

Answer

Typhus

Answer

Dengue

Answer

Malaria

Question 8

Which Entamoeba species is morphologically identical to E. histolytica?

Accepted Answer

E. dispar

Answer

E. coli

Answer

E. hartmanni

Answer

E. gingivalis

Question 9

All of the following can cause obstruction of the hepatobiliary system EXCEPT?

Accepted Answer

Ascaris lumbricoides

Answer

Ankylostoma duodenale

Answer

Clonorchis sinensis

Answer

Fasciola hepatica

Question 10

Most West Africans and people with origins in that region carry the Duffy-negative FyFy phenotype and are therefore resistant to______ malaria?

Accepted Answer

P. vivax

Answer

P. ovale

Answer

P. malariae

Answer

P. falciparum

Parasitology — MCQs

Parasitology — MCQs

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